in my opinion after looking and shooting both of these guns an upped ion would effectively be cheaper and CAN be better if as others have said you spend your money wisely! With a PMR all you really need is a new back cap and barrel trigger is personal preference so not a must have piece of kit! so with that said....
PMR £250
Back Cap £17-19
Barrel: £40
total: £300 ish
With the ion you will need one or 2 more upz but in my opinion the only one that are a must have is..... an oops,Qlok, Barrel, fire bolt. i dont see the need for a new board as a ion can ramp and have semi and it shoots more than fast enough!
ion: £150
oops: £25 (CP oops cheepest ive found)
Qlock: £20
Barrel: £40
Fire bolt: £28
Total: £263 (£37 cheeper than an PMR meaning one extra training or you could get a QEV and some pimped hybrid grips for around the 300 mark)
So it comes down to this.... if you wanna up your gun and have some fun whilst saving a bit of cash the ion is the way! (also it is more than proven not only in training but in major league tournys theres allways some one playing a CC or wateva with one!) Or if you wanna go for a nicer looking better put together model with some allready nice upz go for the PMR another adantage is out of the box it is lighter than the ion.
So once again its a personal preference choice i personnlly prefer the ion just because i own one for a long while and they grow on u
Good luck deciding!!