It all fitted very well with everything lining up perfectly. Bumper cutting was easier than expected (a Dremel with a small sanding drum on the end to finish it off makes a nice job of it)
However, having fitted it I find that the towball is at about 470mm off the floor which means my very standard Erde trailer is distinctly nose up/tail down. To be level the towball would need to be at about 380-390mm.
The rule is apparently that the centre of the towball should be should be between 350 and 420mm off the floor [b]when the vehicle is fully laden[/b].
Even if I sit in the boot of the car it only drops by about 15mm which would mean I'd need several hundred Kg in the back of the car to get it anywhere near level - which is clearly not very practical (!)
As with all detachable towballs you can't adjust the thing and nor will they sell you a different towball arm (because type approval only applies to the specified arm
) . So I enquired as to what height a Brink (Thule) detachable would come in at & they tell me it would be even higher at around 500mm unladen !! 
For just pottering around to the dump etc I wouldn't be too concerned by this but I will be driving over 1000 miles with the trailer on the back with camping gear & 4 bikes on top of it - so it wants to be level (if not slightly nose down) for stability on the motorway etc.
The solution is going to be to modify the trailer's drawbar which can be done fairly easily I think - but a pain in the neck to have to do.
On the electrics side, I bought the Toyota kit & that is fairly straightforward to fit although its not entirely what I would describe as "plug & play". You actually have to extract three wires/connectors from the rear light plug on each side and that is much easier said than done - much cursing & fiddling around with a small screwdriver trying to prise the connections out . Toyota could make that MUCH easier.