I have one of these and it works well.
Build wise its very solid and the bracketry is very good if a little fiddly to install. They use the same brackets for the rack whether you have the backrest or not and it bolts to the fender as well as to the two seat bolts.
I think cost wise its too much for what is basically powder coated bent / welded tube but there are very few options on the market and it is definitely solid.
I have a 25l rucksack with straps running to hook points where the fender bolts used to be. It can definitely hold something bigger and heavier than my rucksack but strangely it comes with a recommended load of 5kg. This seems crazy as the fender itself is obviously capable of taking body weight. I'm not sure how the weight limit would be enforced or be a danger as I'd probably break the fender before I could bend the rack.
I went for it so that I could take the seat off, still carry luggage but not worry about scratching the paint, it also still leaves me the option of going for their C-bow side bags.
Mods so far;
Changed the brick to an oval tail light.
Replaced pillion seat and pegs with luggage rack.
Changed headlight bulb for Philips RacingVision +150% H4.
Changed levers for 7 Click GP Adjustable Levers.
Changed the filler cap bolts to Red.
Added Grip Puppies foam covers.
Added left side swing arm bag made for Harley Sportster XL1200.
Added mesh screen in front of radiator (thanks to JimInOz for howto)
..more to follow..