Hmmm...
Well...both are spool valve guns.
Both have plastic and or low grade parts, that are there to be upgraded as your pocket and inclination allows.
Ion is significantly cheaper than the PMR...buy about £100.
However...Proto, I would say, would give you a better gun for your £250...and you can upgrade teh few plastic parts easily enough...also, teh whole body of teh PMR is aluminium, unlike teh ION.
Have a look at some and see what you think.
PMR would probably be softer on paint.
Or...you could use your £250 to buya secondhand ego...which would pi$$ all over bothe the Ion and the PMR