As an able-bodied (please don't judge my terminology; you know what I mean!) guitarist vocalist, I am already built to carry a sizeable bit of kit (be-it a guitar or a case etc) in each hand as standard. Add a back-pack (again, guitar, computer case etc) and that's three sizeable bits of gear I can carry a reasonable distance in one go. If I need any more then it's multi-trips to the car which not only takes time but compromises the security of the equipment left at either end. Choose the right size RocknRoller and you can get all your kit into the venue in one go and minimise the risk of gear going 'missing'! Oh, and of course, minimise the chances of back strain.
To cover all bases, I would have like the R12T. But listing the kit required for my various work scenario's (and physically stacking it in piles!) I figured that the R6 would be just right... and it was! I also considered the folded size (the R6 fits into a standard large-sized suitcase for international travel/ gigging) and weight (bigger trolley = more weight = more baggage costs!). If neither of these factors are a consideration then I would advise going as big as you can afford.
I use it both in 'handtruck' and standard modes depending on what needs to be shifted. Sure, bigger wheels would have been handy in some situations but again, it's back to that weight/ size thing. At least I am glad that I got into RocknRoller after they introduced the solid tyres (the pneumatics sound like a real deal-breaker). I use a handful of Halfords-style luggage bungees to keep everything in place.
I have to say that I have not any problems with assembly/ build quality but then again, my kit goes in the back on my car and not a van. Further to this, it is only ever handled by me and not over-enthusiastic roadies/ groupies! Every cloud...
For reasons of comparison, my biggest load on this cart consists of 2No. HK Audio 210 subs, 2No. HK 08 tops, 4u amp/ processor rack, mixer/ cable case, pedal board & stands bag. I know it sounds sad but my RocknRoller has literally changed my gigging-life! The only slightly negative thing I have to say is that I have seen big, juicy. extra-long, extra-thick RocknRoller brand bungees on some American sites but I can't see these as stock Thomann items; is there any reason for this?