Yes - I used an Angelsounds one, got it off Amazon, was cheap and cheerful -
I heard a HB from about 10 weeks, IIRCC. I think the point about not using them as medical reassurance is valid - if I had ever had any concerns ever during pregnancy, I would not have relied on it for any information.
I just found it really interesting - I never confused my heart rate with DS's heart rate as his was so much faster, mine was a great lumbering rhythm in comparison - you can hear all sorts in there, from the 'galloping horses' heartbeat to placental swooshings, and later in in pregnancy, the sudden 'doof' of a kick, which always made me laugh. And it was fascinating finding the heart rate in different places as the little bugger moved around.
My DP liked to listen in when I found a hb, and I think it helped him bond a bit with the baby during pregnancy.
So yes, as a 'toy' it was great fun, but I wouldn't use it in a medical way as 'reassurance'. If I hac any concerns I would contact the MW asap, not get a doppler out.