Long time lurker chiming in here.
I've got a Trident Stowaway II and my package from cell_man is hopefully on the way right now. The Stowaway is one of the cheaper trikes on the market and there is no way I would describe it as unstable at any speed I've hit so far. I think people see two front wheels and one rear and assume that the back wheel is going to have less grip.
Downsides to a trike
- You sit low, without a decent flag you are below the window line of cars, so unless they approach you from behind there is a fair chance they won't see you.
- No suspension does give a harsh ride, but the frame does flex enough to help with that. Remember you can't stand on the pedals when a big bump is coming... Big Apple tyres are very popular on trikes to remove the harshness from chip seal roads, but I haven't had a chance to try them out.
- Getting on and off is slower than a DF bike because of the low seating position.
- You can't bunny hop over kerbs which can limit escape paths from SUVs.
- They are bigger and harder to secure than DF bikes.
Upsides to a trike
- Handling, I have managed to lift a front wheel once when I first rode it. Once you remember that you have to lean into corners, the limits appear to be courage rather than traction.
- Comfort, sit on the couch and put your feet up on the coffee table, that's what your riding position is like.
- Braking, twin mountain bike brakes on 20" front wheels combined with a low centre of gravity give you a ridiculous amount of braking power. It makes DF bikes seem downright dangerous by comparison.
- Aero, my partner has a basic Chinese ebike, she can take me uphills and keep with me on the flats, but on the slightest downhill I'm gone. Once I put my motor on, I don't think she will want to play anymore
You do get a lot of attention on a trike, not sure if that's an upside or a downside...
Edit - Forgot one huge upside, crashing. A large percentage (60-70%? - I can't remember where I saw the figures) of cyclist hospital admissions are single vehicle accidents. If you do have a big accident on a trike, you don't have far to fall and you won't go over the handlebars.