Similar but different, slow cookers use low heat over a long period of time where the one pot uses very high temps over a short duration.
pressure cookers ( one pot) are sealed units so there are no , or very few odours if that bothers you. Personally, I want to smell what I am cooking.
both are versatile....you can cook rice, bread etc in both.
the insta pot is good for those who aren't organized, don't like to plan their meals or who might be very compromised for time. Food texture and taste isn't different between them. One thing that might be different is the breakdown of nutrients, should be less in the quicker cook method of the pressure cooker vs a slow cooker if that is important to you.
I don't own a pressure cooker but have used them in rentals and at friends....i do have a slow cooker and use it quite a bit. I see no need or advantage to getting a pressure cooker.....its a time saving piece of equipment....much like using a microwave vs an oven to cook food,....i have all the time in the world and like to plan out and cook nice meals.
they also take up a lot of space and I don't have any available counter or cupboard space.