I use a Superstroke countercore, but I've put a backweight in my putters for many years now. I did a fitting back ~ 2006 and I had a backweight in my putter and the fitter said "do you really need that?". I hadn't used it long and wasn't sure, but we went through the fitting and he finally said "yup you're better with the backweight". I have backweights in all but my 8-P, SW, GW and LW.
Sometimes I just put a backweight from Hireko/Value Golf in the shaft and then use the regular Superstroke Flatso 1.0 that I like. It's the same either way.