It's 'Piston' class in both the BFTA Grand Prix's and the WFTF World Championships so if it has a spring/gas ram and a piston then it's in Piston class. Some regions exclude SR's by having a 'Recoiling' class (NEFTA for example)
So in short, yeah you can shoot a TX200 SR, Diana AirKing, Whiscombe etc in direct competition with real
springer shooters, but there's no honour in it
It sounds like you're falling into the trap that a lot of people fall into when they first start out at FT, you've gone through 3 guns and it sounds like you're considering a 4th before you've shot in your first competition.
When it comes to competition success, I'd say that 30% of that success is down to your gun/scope/pellets - 70% is down to the person pulling the trigger.
You'll progress quicker if you concentrate on the largest part of the equation.
Practice, Practice, Practice is the key, and if you want to be good in competitions, the best practice is to shoot as many competitions as you can. Competition shooting is about far more than just shooting ability.
Why don't you plonk a scope on that LGU and get yourself down to GP5 at Blaenau Gwent in a couple of weekends time.