It's basically a bike with a battery attached. You should have enough battery to last you all day but there are peddles if you run out. We found it useful to hire one of those around 6000kyats a day I guess to go further afield to the temples further away. You can cycle but it takes awhile and if you are there for sunset the e-bikes are great to get you out of the bush quickly. We went to a temple off any main road and we were glad to have the e-bike as it was almost pitch black by the time we got on the main road. A torch of head lamp come in handy as the bike ones are useless.
When I was in Bagan last year, there was no e-bike to be spotted.
After a long day riding a bike in the sun, I even thought to import some e-bike there as I have a friend working with a Chinese E-bike factory.
I think the person who did it was right, it is very hard to ride a bike all day long in Bagan and I also think that taking a car or hiring a horse cart are too expensive option.
Did you get your bike from your hotel or a specialized shop?