I used an electric trolling motor for a number of years, on both an inflatable dingy and then our 10' portabote. I don't know what hp it was ... not big I'm sure. It moved the portabote reasonably well, but not surprisingly performed poorly with the heavy inflatable.
I went to a 3.5 hp gas outboard mainly due to the limited range of the electric, and the challenge of keeping the dingy battery charged. For short runs ours was fine, but if we wanted to go far, or to fast, we would drain our battery pretty fast. I also played with a Torqueedo for a short while on our Portabote. This had all the power I would need, but again I found the battery got drained rather quickly. Then we were back with the challenge of charging.
For me, I would much rather have an electric over a gas outboard, but until the battery technology improves, it's just not feasible for our cruising.