NOOOOO!!!
I was unsure, like you, and in the end decided to buy Angel Sounds for £50 as I had heard good and bad reviews.
I was so excited to hear the heartbeat (I was 12 weeks, and instructions said I would find the heartbeat at this stage)
I spent the whole weekend trying to find the heartbeat. I couldn't find it at all.
Ended up having a huge breakdown, crying my eyes out, convincing myself something had happened and almost booked another private scan just to put my mind at rest.
I had my scan booked in for the Wed luckily, and thank god, the heartbeat was strong.
Turns out I have a curved womb, and so chances of getting the heartbeat on a doppler was close to impossible.
They advised me at the hospital to throw it away, as they cause so much worry and stress.
She said it can be very difficult to find the heartbeat if untrained, and this is why they strongly recommend not to get one.
My advise would be listen to the Midwifes, and DO NOT buy one. It honestly caused me the most upsetting and stressful weekend of my life!!