I have a Catrike Expedition with an 18 speed Pinion Gearbox up front. My knees are not what they used to be. I need an e-assist. I will need a hub drive if I want to keep my Pinion. It’s like have an automatic. I can pick any gear I want stopped or moving. In checking with Grin Tech none of their speed sensors will work with the Pinion. I prefer a torque sensor anyway. The only torque sensing hub drive I have found is made by Falco and ridiculously expensive. I still don’t have good grasp of how a hub motor works. If the hub motor spins at a set rpm, what’s the point of having any gears at all? Although as I think about it, the gears may be used to keep the bike at the motors rpm? With the 10-speed cassette in back I have 180 gears to choose from. Looking for some ideas.
What an wonderful bike - and that Pinion gearbox sounds great too. You really don't need the rear gears so a hub motor looks like it would be the easiest and most obvious fit.
A lot depends on 2 things - firstly, the kind of riding you do. Is it for commuting, touring, adventure, daily transport or occasional fun?
Secondly the terrain you will use it on. Is it flat, undulating or hilly?
Hub motors will handle a few small hills fairly well but struggle with long or steep slopes. If you will be riding on mostly flat then a hub motor with a throttle would be a good, cheaper, option. They have a lot of advantages.
A crank mount motor would seem to mean the loss of that terrific gearbox, but would be more needed if you had a lot of hills to ride up.
As you say, a torque sensor would also mean the loss of the gearbox and not being able to use a hub motor. I haven't had a bike with one so I haven't experienced their advantages but I do have a well programmed cadence power assist and it is very smooth and I feel I have good control.
I'm not sure I have added anything new to your thinking but good luck with your deliberations.