this spring i would like to get a tag-a-long for my 4yr old. my lbs can get burley, adams, and sun models. i would like all feed back on these models and especially the sun. of course i will also be looking on craigslist for ideas as well. thank you all and have a great holiday season.
Burley Piccolo is by far the best tracking tag-along.
The connection sits in the middle of the special rack and tracks the tandem 100%.
Others have a tendency not to track near as well and if you don't watch it when going around a corner the tag-along could clip the curb.
I can give you my reviews, but your experience may be different depending on a few factors. We have a Burley Kazoo (the single-speed version of the Piccolo) and love it. It's extremely stable and the accompanying rack allows for use of panniers while using the trail-a-bike. We tried a seatpost-mounted Alleycat first and there was just way too much play in the connection (also, we didn't have enough clearance for a rack under it). It was far too easy for my daughter to tilt the bike from side to side and throw me off balance. We have friends who had the Adams trail-a-bike and had a similar experience.
I think seatpost-mounted systems can work okay if you are a strong cyclist and there is a large weight differential between you and the trail-a-bike rider, but if you have the money and you want a system that works really well, I'd go for a Burley. The initial price is higher, but the re-sale value is much better (based on what I've seen on craigslist, used Burleys sell for at least 50% of the original retail price). As between the Kazoo and Piccolo, I don't know that the gearing is necessary; we just spent the weekend in San Francisco with our bikes and my husband had no trouble making it up high hills in his lowest gear even when it got harder for my daughter to pedal.
We have a Weehoo too (I've bought way too many kid-biking set ups) and while I think it's superior to a trailer for kids from 2-to-4 (though my top choice for that age is a bike-mounted seat), I think a regular trail-a-bike is a better option for 4 and up for several reasons:
(1) A regular trail-a-bike helps teach balance and position to ride independently
(2) The Weehoo is heavy and harder to haul
(3) While the Weehoo is more stable than other seatpost-mounted trail-a-bikes, it is far less stable than a Kazoo or Piccolo
(4) The Weehoo sits down low and is long, which makes it hard to see in an urban environment, even with the flag.
(5) Because it's longer than a regular trail-a-bike, it's hard to maneuver
Upsides to the Weehoo:
(1) Easier for kids to rest on long rides
(2) Less fear of falling off because of the seatbelt.
I would only consider the Weehoo if you anticipate going for very long rides or touring with your kids (there's a couple online who took their Weehoo on an Asian tour)