after my wife read on the internet that she should feel kicking at x weeks, and couldn't she started worrying, so she bought a simple doppler listening monitor off the internet. It did put her at ease, she has used maybe a handful of times.
I was against it, as if the worst happens, we're alone at home to discover what might be, then we would have a horrible wait, whilst the hospital confirmed it.
The key with it, is for the barrier cream to be applied in abundance, and you do need to be sure where you pointing the thing.
If your Doc suggests not to get one, then I would hear their advise.
p.s ours cost less 15quid, but we do live in China