Sorry for the delayed response, Jelopster, but I have a lot of thoughts on this type of question, and some of them are contradictory, so I get mixed up. It also leads to a long response, so buckle up. (Or not, and just disregard, meaning that I just wasted some time.) 🙂 You could just read Valuegolf's response "No" and basically end up in the same place with more time on your hands to play golf.
My biggest problem with a question like yours is that I really don't know what an upgrade means in terms of golf equipment. I really don't.
Too many people think that an upgrade in equipment has something to do with brand or price. As a result, I see far too many people shooting 110 with $4000 of equipment in their bag. Even here I'm sympathetic because I think you do, in fact, gain some confidence from having a set you're proud of and somehow "believe in." I always say that I think your shot begins as your approaching your bag and pull the club, and liking your clubs is part of that. But that type of Poon wears off quickly (it's kind of like dating, but I'll leave that comparison alone.)
I'm also conflicted when it comes to price. While I am a HUGE believer that you can't buy a game and that price is meaningless, I assume (maybe incorrectly) that my clubs are going to outperform a $99 full set of clubs that I can buy from the local hardware store. Assuming I'm correct, that means that there is a breaking point somewhere on the brand/price scale.
But if you have a set of irons that has a modicum of quality in terms of design and manufacturing, then I'm not sure how to differentiate between one iron and another. The only way to distinguish between irons is how you feel about them and how they perform for you. If you have a set of clubs that you hit in the centre of the face and that you enjoy hitting, I don't see how you are going to benefit from getting a set of Honma, PXG, Miura, etc. In fact, you may hit them worse. Have you "upgraded"?
Since you asked for my personal experience with the two, here are my thoughts (remember that my 1Irons are more than 10 years old and my In1Zones are at least 4 years old, so there may have been changes that make my observations inaccurate).
I don't love either of them. I would give the edge to the In1Zone though; IMO the cavity in the 1Irons look cheap. I like the look of the Pinhawks, but there's no love there, either. My preference would be the Wishons, but that is a completely personal thing.
Over the ball
Both have a fair amount of offset (about the same, I think). Many people seem to associate less offset with a "player's club," but it's more about personal preference. I like quite a bit of offset because I like the way it "frames the ball" at address. But a person doesn't like an offset would consider this a downgrade.
I prefer the 1Irons because they have sharper lines, a sharper leading edge (I believe), and a thinner topline. I like all of those things. Again, a lot of people associate these features with a "player's club," but that's not true. They're personal preferences, not an upgrade. Which do you prefer?
Forgiveness and Feel
Both are really forgiving clubs. I think I would give the edge to the In1Zone, but I'm not sure if that is fair or not. To me, the 1Irons feel a bit "clickier." But this isn't really an apples to apples comparison since I have completely different shafts and grips on the two sets. I was going to put the 1Iron heads on the graphite shafts that I have in my In1Zone, but decided not to for reasons I will describe further down.
On the flipside, I do prefer the feel of the 1Irons because they give me better feedback on off-centre strikes. I can't tell where on the face I've hit the ball with the In1Zone unless I really mis-hit one. Now is that a big deal? No. But my preference is to get that feedback. For others, that may be a weakness/downgrade, particularly if you are really inconsistent with your strikes.
Don't even get me started on this. I hate when 90% of amateurs talk about workability. Most of us should never try to work a ball unless we're just out for fun. In fact, the less workability the better for most of us. I'll try working a ball on occasion, but when I do, I'm trying to get out of trouble. And about half of those times, I'm in even deeper trouble after the attempt.
Customizability (Is that a word?)
This is the big one, I think, and it applies to all clubs, not just these two heads.
As I have been alluding to throughout this post, an "upgrade" is really dependent on preferences, suitability, and performance, nothing else. And that doesn't come with price or brand. You want to get a grip you like, a shaft that is the right weight and length (flex and profile is a distant third), lies that are right for that club length and your swing, and lofts that make sense. If you're willing to pursue those with a fitter, then that's where an upgrade can be found. But, in fact, I think this is where 1Irons/Cobras (and possibly SMT since I don't see a heads only option for them) actually become a downgrade to In1Zones/Pinhawks/Wishons.
1Irons are "fit" to wrist-to-floor measurements over the internet. While I think this is superior to an off-the-shelf option, it's a very poor cousin to an actually customization. Now, don't get me wrong: I think fitting can be taken too far, but grip/length/weight/feel should be addressed. That's an upgrade! But that requires trying out different options in a strategic way, which is what a fitter can do for you. Just don't get sucked down the rabbit hole.
It's here where I think the 1Irons begin to fall down. They have NO grip and shaft options. David Lake claims he doesn't believe that makes a difference for most golfers. I couldn't disagree more if I tried. (Let's see if I can.... Nope, I tried, I really did, but I couldn't.) Not only that, but since these irons are made from 17-4 steel, you can't even adjust them much. That's a big drawback for me. As I say, I would like to put the 1Iron heads on the shafts that I use, but because of the specs I play with, I'd need to adjust the lies quite significantly. I can't do that with these heads.
In1Zone/Pinhawk/Wishon's heads are made for customization. Not only can you put different shafts in them, but they bend really easily, so you can adjust the lies and lofts appropriately. That's important! You may not be doing this work yourself, but IMO it really needs to be done. In fact, I think it's more important for SL. If you get the setup correct, you have a full set that fit you. But the opposite is true as well -- get the "wrong" specs and you now have 8 irons that don't suit you.
Customizability is particularly important for the In1Zone because unless they've changed things, their lofts are whacky. Dave Tutleman once said that they would be the best SL set on the market in his view if their lofts made more sense. DTG golf responded by saying that their lofts can be easily bent (which the can!), which led Tutleman to upgrade his assessment of them.
In the end, if you can get fit to a degree where you are comfortable with your set, you like the look of them, and they perform for you, then anything else is just fiddling around and trying new things for fun...it's not an upgrade.
That's just how I see the world. 🙂