I had one fitted on my XRL, when it seized in Spain (in temps of about 43C). Pretty yes. Useful? Probably not.
In my experience it didn't really help, for 2 reasons:
1)When something disastrous happens (like oil pump failing or a piston ring popping) the oil temp spike is so quick that you'd have to be constantly watching the little dial to notice. Noises from the bike are far moer obvious!
2)Having the guauge makes you complacent. Mine was severely underfilled by a garage and the oild droppped off the bottom of the dipstick in the course of a single day. As soon as the sensor was getting the ambient temp. in the oil tank, the needle went back down to normal operating temp. Bad news.
For my big trip I think I'll install an oil pressure sensor with a really bright light / buzzer or something. Much more useful. Anyone done this?
They're damn hard to see once you have a big tank, barbag, barpad, tankbag, GPS, enduro bottle etc etc etc.
The only thing I ever really used mine for was quantifying how useful my oil cooler was, and finding out when the bike was warmed up properly.