I have one of these ones,
http://www.ebay.co.uk/itm/310760589990? ... EBIDX%3AIT" onclick="window.open(this.href);return false;
works well enough, but the viewing angle isn't that wide. The camera is mounted inside the bus, top of the rear window looking down towards the bumper, can't see the bumper but you know that if something is about to go out of view then you need to stop.
Monitor has a second video input, can be used for DVD's or headunits with composite outputs etc.
Unfortunately the T25 rear view mirror is too big for it to clip onto, which is a blessing in disguise because if you were to fix it there then you have no mirror as the LCD isn't mirrored when its switched off (some are).
The Wireless makes it simple and works well, no interference etc, but you still have to route a reversing light signal to the front of the van to turn on the LCD, I've re-used one of the redundant wires from the original loom (alternator warning light) when I converted to TDI.
Dave.