It makes a difference in shot consistency because having a bearing on both ends of the spring allows it to coil as it compresses and decompresses.
Haven't seen the actual info in years, but I recall it was quite noticeable.

However most pistons allows normal operation and never have issues. I only see maybe 1 in 10 guns now that don't have bearing spring guides.
But this is why it's bad to mix brands, or choose low quality brands. Either the QA is very poor, or the parts are proprietary.

are you test firing the gun without the stock on? because if you are, thats most likely why the spring guide is moving. the stock screws into the rear of the spring guide to hold it in place. Without it, the V2 spring guide has a large chance to move around.

Also have you tried just using the stock motor with the 9.6V battery to see if theres issues there. My history with hi-speed motors are they eat gears and pistons.

G&P M120s aren't 'high speed' motors, they're just labelled 'high speed'

I did the test firing with the stock on. I tried the stock (Aftermath) motor with the M120 spring and 9.6v battery. The stock motor wasn't able to move the gears. Replacing the motor with the G&P M120 motor allows the gun to fire with a good rate of fire.