It's may be worth potential users knowing about running costs even with these guns. The Senco and Milwaukee guns use a factory pressurised nitrogen cylinder which has a certain life before it needs to be replaced (because it loses all pressure). My understanding is that this isn't cheap. Don't k ow how reliable the 2and generation Milwaukees are, but the first generation had overheating issues when bump nailing (presumably hence the redesign) whilst the Fusion has a bit of a chequered history (with sticking drive pins, misfires and mode lock being common problems)
Hikoki guns use compressed air which when it finally discharges can be repressurised by a Hikoki service centre, a cheaper process. The Ryobi is a bit plasticky inside and probably not suitable for intensive use (see the YouTube strip down of one by AvE)
I used DW guns both 1st and 2nd generation for well over 10 years (in the case of 2nd fix, 5 years first fix). They are different to gas nailers, mainly heavier and bulkier, but "not as nice" doesn't really explain your objections very clearly. Could you please elucidate them?