I was going to say the same about Prime, but it's not perfect either.

Their Windows app is terrible. It takes forever to start for some reason. Sometimes, after a few minutes, I just give up and launch the browser. Sometimes if I try to get back 10 seconds it will just freeze playback. I can sometimes get it back by trying to fast-forward around. Others I have to stop watching and start again.

This never happens on the web app.