John, all the various barrows out there are purely versions of the tried and tested builders wheelbarrow. The only difference is usually the type and size of the load platform. The riggers barrow that Sam uses is just a simple flat platform, which is light and adequate. Others have the more fancy design platform with fronts, backs, sides and a friggin teasmade if you are lucky
The only issues are when they try to reinvent the wheelbarrow. A single central front wheel set reasonable well back, to take advantage of the lever principle, with handles and rear legs all designed like a builders barrow, is about as efficient as it gets. Once they start fannying about with that, putting the wheels nearer the front, using two front wheels, weird handle designs etc., etc., then that is when the problems start....they are pants.
My advice is to go with the basic design, with as much weight as is feasible in front of the wheel. That gives you balance and significantly lightens the load as said, and the single wheel helps with keeping the whole thing upright on uneven ground. All you need then is to choose the strength versus weight ratio that suits you, and you're done. The Carp Porterlite Mk2 looks good, though I haven't tried it. It is light, looks well designed...and is less than £90. Must be worth a look?
Cheers, Dave.