I fitted a conversion kit to Maz's Dawes Geneva (Step-thru hybrid with 7 speed shimano hub gears) as she has arthritis in both knees and was so impressed that I wanted one for dragging the trailer up the hill/ridge we live on (the trailer sometimes carries over a hundredweight when I'm doing some 'landscaping' or fencing)
That plan got put on the backburner when I broke my femur but I expected to be back on a bike in 4-5 months unfortunately I needed a second op (remove the pin then drill out the bone and fit a bigger pin) and as part of the physiotherapy I was put onto an exercise bike at the hospital and the guy said "its a shame you have'nt got one at home" so I toyed with that idea and also getting a 'turbo trainer' and bolting one of my bikes to that but then got my trike. Only problem was that I then couldn't get up the stupid (

) hill on it limiting me to cycling along the ridge and back so the Trike got modified so that I could fit a 26inch electric front wheel kit to that (the standard front wheel was 24 inch but if I'd got a kit that size it would not have gone onto the MTB later, plus I'd have had to change the forks anyway as the dropout wasn't thick enough to accept the anti-rotation widget on the electric wheel with the standard forks)
The only snag now is I'm starting to like the trike as it is so I may need to modify the trailer hitch so that it can be pulled by the trike (the hitch clamps on to the chainstay and the trike has an axle in the way

)
The only downside to electric bikes is the cost of the battery pack, I looked into getting a second one and they are £240 so if anyone thinks of getting a secondhand e-bike that cost needs to be figured in as they have a lifespan of 3-4 years and there does not yet seem to be a standard so most are specific to one particular brand.