Just after we crossed the cycle bridge over the Esk in Musselburgh, we saw a weehoo trailer. It's basically half-way between a tagalong and a trailer
Interesting. Kid in it clearly loved it and his Dad thought it was fab.
I'd checked out something similar when K. started getting too small for her bike seat, but am glad I didn't go that way. Basically, it is more trailer than tagalong, but less versatile. I can see it appealing to parents used to having kids falling asleep on the bike. I was definitely worried about that, and the idea of still being able to strap'em in has appeal.
I suppose the weehoo is slightly narrower than most trailers for kids, although its bulky enough that they still struggled a bit to get through the barriers (not helped by me being stopped at the bottom).
But the good thing about a trailer is that its useful as a trailer as well, not just as a child carrier. But at more than twice the cost of a tagalong, I'm not sure I'm convinced. Perhaps for those on not too much of a budget and/or planning to resell.