ION is simpler in terms of off comes the back cap and bolt is out, not as much compared to the pmr and slg bolt kits, the ion is heavier and the pmr is the only one that comes with a respectable barrel, the pmr trigger is the best imo. There are plenty of functional upgrades, feednecks, asa etc, for all 3 guns. They are all reliable and shoot fast enough, but the pmr takes the cake in terms of value for money, in most cases its the same price as the ion. If you want to take you pmr to the next level, the SE version is £199 and the pmr with UL frame is also £199, i would get the UL.