I honestly have no idea what the advantage of propane would be. Even if you have it on board already, are you going to unhook the can from your BBQ to use it on your outboard?
I feel similarly about the torqueedo. I know people like them, but they have limited range, are costly and not that powerful. Also, I have to think charging them on the hook would be problematic. I follow a YouTube vlog with two sailors who have one and rave about it, but when I watch their videos and compare it to my experience with outboards, I always think "that thing sucks."
Small gas outboards are a proven commodity and a tiny one like that would burn almost no fuel.
FWIW, I'd just get a bigger outboard. At least a 5hp. Not that much difference in weight, cost or fuel burn. Lots of situations where you can have too little power, almost none where you have too much. It's a safety thing even.
I'll get off my soap box now.