I really liked the tstick, too, so I got one and used it for a little while, but eventually decided that it was crap.
On the Happs joysticks, the handle is held on with an awesome little c-clip. It's perfect, as far as I can tell.
The tstick handle is like a big bolt and it's held on with a nut. It's a pain to tighten because the harder you tighten it, the more difficult it is to steer the joystick. The end result is that you can't make it really tight so that it's held on very well. Of course, as you're playing, the joystick spins around a bit and loosens the nut until it falls off. When I played on it, I would always be thinking about it so that I could twist the joystick to tighten it again. Other people were not so careful, and every once in a while you'd hear the sound of the nut falling to the floor. A couple of times someone would be playing and they'd yank the handle right out of the joystick (when the bolt was off).
So from my experience, the tstick is a piece of junk. I'm sure that somebody has a good way to keep that from happening, but I didn't bother with it. I just scrapped it and got a 4-way joystick separate from the 8-ways.
The problem with the switching mechanism is that common users of the cabinet don't understand the 8-way vs. 4-way dilema, so they don't know about the switch or when to use it. They'll sit there playing Street Fighter in 4-way mode and wondering why the controls don't work.
Finally, the last weird thing about it is that it's incredibly stiff. It takes a decent amount of muscle to move it in the direction that you want. That could be a good thing, but I think it's better without that much resistance.
It sucks because it seems really sweet, except for that nut thing.