I got one at about 11 weeks and I was so upset when I couldnt find my babys heartbeat! At about 14 weeks I could hear it loud and clear! Some ppl can hear it early but I wasnt one of them. if you do get it now try not to get your hopes too high or freak out if you cant hear it.
I returned to one I got. I found I was more stressed out because i could never find the heartbeat. It just made me worry more and now that I can feel the kicking & movements I didn't see a need for it.