There seems to be two main variations around similar designs. The first is the Towsure/Towtrust/Ecco type , which only requires that you drill one 'new' hole in the vehicle, which is under the trim strip exposed when you open the tailgate.
The other type ( I can't remember who makes them) requires you to drill three new holes through the chassis rails, plus the one up through the body at the rear, as per the 'other' towbar variant.
Having just fitted the latter type of towbar, I would offer a few simple words of advice . Buy the first type
It's bad enough to have to drill (and open up to approx 16mm dia) four holes through chassis rails, and ensure that you get the appropriate corrosion protection in place but I also discovered that either :
a) My Bongo has exhaust heatshield mounting and existing chassis 'nutserts' in the 'wrong' place
or
b) The towbar I got was manufactured with rather scant regard for either initial accuracy in it's design, or reasonable tolerance specification during the fabrication process.
It didn't line up with the two nutserts in the chassis at the nearside, or the two holes that you use to bolt the heatshield to the chassis rail, and had to be 'reworked'.
I've fitted lots of towbars, and not once had to drill a single hole in any vehicle in doing so, and, before anyone shouts at me for not doing it right , I do have at least the beginnings of a fundemental grasp of engineering principles
The only positive thing I would say about the type of towbar I fitted, is that it is so substantial I think it would even cope with 'snatch' type vehicle recoveries. Unfortunately, I may need to adjust my headlamp alignment as I'm sure the Bongo is sitting down by a bit at the stern, due to the extra weight
