Thought it might be better to train in one of these as when I am qualified I can immediately start sharing costs 4 ways to build hours. I also think it might be better for experience to train from a bigger airfield with full air traffic control.
I agree with all that has been said, and there should be no problem with changing schools. I'm just not sure about your reasons for doing so.
Cost sharing. In my experience, friends want to come flying with you and pay their share...once! Most people run out of cost sharing friends very quickly. Unless you know this will work in your case, don't assume it will. What often DOES work is cost sharing with another PPL, and swopping the flying and nav/radio. And a two-seater aircraft is fine for this.
ATC etc. In my experience, those who learn at a big airport are better with coping with the radio, while those who learn at a small one are good at making their own decisions, fitting into circuit patterns sensibly etc. But it all comes out in the wash! Either school will take you to one of the other sort for practice, and you can easily fly to other airfields to practice after you get your PPL - it's not a big deal.
Conversion from a C152 to PA28 once you've got your PPL is not a big deal - probably a couple of hours training.
So change school by all means, but base your decision on the quality of training, rapport with your instructor, and general convenience of the airfield for you, not things that probably don't matter that much.