"Trailer bike" reviews/recommendations??

No experience of actual use but my local LBS was selling these:
http://www.trail-gator.com/
It's supposed to allow you to quickly convert a childs bike into
a "Trailer Bike" and back again so the littlie can ride when it's safer.


After riding this one the kid will want to be riding with a non stop mono!
Looks kinda fun. Someone mentioned before that they wouldn't attach one of
these to a road bike. I don't think I would either, and I doubt I even
would with my good mountain bike. I know my mountain bike is very strong,
but I'd be concerned about possible frame damage. I'm sure it'd be fine,
but I'd still be a little concerned. I don't have kids yet, but I've
considered getting a cargo trailer. I've never bothered because I was
mainly wanting it for off road mountain biking camping trips, and in the end
I've decided to keep the load on me and the bike instead because I'd imagine
a trailer would get annoying on rough trails. Has anyone ever used one?

Roger