My 2 cents;
I've had my Greenspeed tandem trike for about 4 years now and still ride it quite a bit. Sometimes solo, sometimes with one or more of the kids on board. I say this this way because I got a nice Greenspeed GTX about a year ago and that has become my main ride since then. My wife is a non cyclist, so she has never even tried it. But the kids LOVE it! My 12 yr old stokes, the 6 yr old ride on the rack (I made footpegs for better stability) and the 4 yr old twins ride out back in the Burley trailer. The Burley is great because it fits perfectly in the rear triangle of either Greenspeed. That way, all the kids ride at the same speed (mine) and go the same place. Haven't lost one yet!
Only drawback to riding the tandem solo is that there is sometimes not enough weight on the rear to keep from spinning the tire on steep roads. I have taken to adding firewood to the back seat to help with traction. Tandem triking solo is good for hauling a BUNCH of groceries. I use the rack, panniers AND the back seat to load it all on. I only use the trailer for groceries when I'm doing A LOT of shopping, because it brings the total lenghth to just over 15 feet. AND it's a lot harder to back up with the trailer.
I also feel safer on the tandem because it is so long, even without the trailer, that car drivers seem to give me extra room when they pass. Maybe it's just so they can get a better look at the thing!
Anywhoooo, hope that's helpful.
Dr.D