We have had a doppler from about 13 weeks and heard the heartbeat. It took a full day of trying, it took hours of trying. I would also like to say this is my wifes 3rd pregnancy and the more you have the easier it is to listen in.
If you feel like getting one I would. We went for a cheap one but soon went for a more expensive hibebe model with lcd heart rate display
A few things I would say before though. Sometimes you won't hear baby because they have a lot of room to play in, can hide behind your pelvic bone or just not want to be found. Our little girl used to be found here there and everywhere.
Its not possible to hear the babys heartbeat from 8 weeks. At that point you can only just pick it up on. A scan. It could be the placenta or cord that you have picked up and thought was the babys heart beat.
I look back now on the last 14 weeks of having a doppler and realise from what I have heard that I am guilty of getting the placenta and babys heartbeat mixed up.
It is so easy to do as the only difference is that the placenta makes a wooshing noise and babys heartbeat sounds like horses galloping. It really is so easy to mix them
I'm not trying to upset anyone, just wanted to say this as I would like to have known when we got our doppler.