I have not used a trailgator, but I was wary of them for most of above reasons. I have loads of use with 6 speed tagalong though. On and off road. Even gnarly rooty descents and climbs are possible if you get the teamwork right. You’d be amazed how much a 6 fit year old can contribute if they have the right gears. I recon we go up hills almost as fast together as I do on my own. The geared tag-alongs are SOO good.
I’d be concerned that on the flat, a trailgator would make it impossible for many kids to pedal and contribute, because they are too low geared and couldn’t keep up at ~ 200RPM. That might lead to some problems and boredom on long rides. My 6 year old daughter gets enormous satisfaction at making a really big contribution to the effort both on the flats an up the hills. Worth remembering.
Also what happens to a trailgator off road if the kiddies front wheel (not very far off the ground) touches down? – What gives? – And is it extra fun if it happens in a corner?