I take it Tri tech isn't the same maker as Andys modern micros?
I can here spluttering from Nottingham from here! No Andy Carter has nothing to do with Tri Tech and I often wondered what he really thought of all the shenanigans.
The Tri Tech Schmitt is very easy to turn over since the suspension geometry is not well designed using as it does an Indespension type rubber in torsion trailer unit mounted sideways. On that is mounted mini brakes with the kingpin to far inboard for efficient use. It breaks all suspension geometry rules without the Colin Chapman effect of working well! So like any trike of that layout it can be made to tip, it also does it randomly as the directional stability is, frankly, brown trousers at about 40-45 mph. Once it starts weaving the non progressive suspension tends to go out of balance, pulling on the steering due to the arrangement compressing the suspension alternately thus magnifying the steering pull and over you go despite steering dead ahead. I have had 4 TT Schmitts, two scrapped one by turn over and the other fire, one turned over, repaired and sold on and the last for a customer for whom I modified the car for so it was safe at 55mph. He has lost his nerve though I think. Another turned over near Andover and was impounded by the Police back when they were being made. Around that time all went silent for TT. By all means buy one but be aware it is a compromised machine for driving. If not for driving why own it? Alternatively save up for a real one.
Less experience of Zettas in action as they refuse to manage to work and yes it took an hour to retrieve the Zetta from that narrow hill near Bath. It might even be the same car that is the one for sale. The problem was keeping the drive chain in tension. As for rolling, I think most Zettas are to powerfull and on radials so it is all to easy to reach tipping point without any warning. Though one rolled as it lost drive on a Hill and turned over rolling back while the drive paniced looking for the problem and brake. This would suggest the drive train assembly is not robust enough for the task as that is at least two cars having the same prob.