Did you mean a trail-a-bike recommendation? The wheel/pedal/seat/handlebars that attach to the seat stem of the adult bike?
We have had two Adams trail-a-bike's for I think 3 years now. We bought one new, and picked up the other at a massive used bike sale. No idea how old it is. They are both GREAT. I read reviews of parts falling off REI's Afterburner, but we've had nothing like that happen and I can't imagine what could fall off. They are very sturdy. Also very easy. After you have put the bracket onto the adult bike's seat stem, taking the trail-a-bike off or putting it on takes all of a minute or two. It's incredibly simple.
Both our kids know now to bike now, but they did not when we started using these. Three is old enough, if the kid is tall enough. One thing we did notice is that we could adjust the older one to a shorter leg-length than the newer one. All the kid really has to do is hold onto the handlebars and balance on the bike seat. We still use them because we can go places much more quickly as a family than with the kids on their own bikes. Plus, they love it. It's a time for long conversations and somehow more observations than in the car. Both my kids sometimes like to propel it without the adult pedaling.
They definitely make the bike feel different, but not in a way that makes me feel any more likely to tip over. The bike sways more, but it feels heavier and less likely to go all the way over. Like paddling in a sea kayak vs. a canoe. I worry much more about cars. Ours came with orange flags, and I have covered them with flashing lights for if we ever get stuck out at dusk. We also don't ride anywhere with remotely scary traffic.
I think they're great. The design is so simple it would be really hard to wear one out, and they are really, really fun. You might be able to find one on Craig's list.