Found this old thread when doing a search, but thought I'd post to it.
I've now had a TrailGator for over a year, and I can't recommend it highly enough. YMMV, but I've had no issues with it at all. Gets used twice a week or more. Solid as a rock. Only a minute to attach/unattach the kid's bike. Took a (very) little fettling to set it up (they have shims to get the angle right) and then you're off. It's a very solid unit, so it ain't light. But then, attaching a kid and bike to the rear isn't gonna get you speed anyway, so meh.
But yeah... after 14m or so still very impressed with what it can provide. So much so, I'm in the process of getting a second mounting bracket, which I'll put on a seatpost that fits another bike, so I can swap around a bit more. Thing1 did 22kms on Sunday, with about a dozen of those on the back.
But, this is why I like it best. From yesterday
Escorting her friend home (about 6km)
...and the return journey.
It really does give you the broadest range of possibilities out there, as you can buy a decent bike that suits your kid. The only warning - there's some kids bikes that I'm told there's just no way to fit the bracket on the front