If you want to use it for reassurance, dont.
If you want to use it for fun or bonding, then go for it!
Its actually very easy to tell the difference between your heartbeat, babys heartbeat and the placenta, though I'd recommend checking your own pulse before starting, so you can be sure.
Providing people dont use them for reassurance, or instead of medical attention, they can be great fun.
I've usually found babys heartbeat from 10-12 ish weeks, though in the early months there have been times I couldn't find it. If that would worry you, dont get a doppler. If you are the type (I am) to just shrug and try again the next day, thinking its probably baby in an awkward position or the placenta masking it etc, then go for it.
Only you know how relaxed you'd likely be, and what you'd use it for.
I wouldnt want to see them banned though just because some people cant be trusted to use them responsibly.