We’ve had one since 6 months and Rose loves it. She’s now 2 and a half, and we still use it, it is pretty much as good as new after well over a thousand miles, except for a few scrapes where I bottomed it out riding down a too narrow track in Shinin, Cliff Woods.
Tons of luggage space – ours has been bike camping twice with all the gear for the two of us in the back of the trailer (and teddy bears, toys, books, nappies etc.) You notice the weight on the hills, but not so much on flat roads – I’ve done 40 miles in a day no problems (Belper to Tissington, Tissington Trail, High Peak Trai then back to Belper). Great for picnics, shopping trips. We have a double, which limits you to wide singletrack, but means you can give friends a lift, which Rose likes. I’d buy single if you were thinking of going for anything super narrow, although round here in Derbyshire I rarely have any problems (and I tend to only take it places where I know the route anyway).
When you first get it, use it a lot, and try to use it at nap time, that way they get used to it, and also learn to sleep in it. Ours is a real baby sleep machine – she’s had three hour naps at times!
Oh and if your baby is young, don’t forget the baby sling, which is also brilliant – Rose grew out at just over one but she was a teeny tiny kid then, so expect it to run out by one or so.