I had a doppler when I was pregnant with georgia after 2 losses I really felt I needed something to ease my mind. A real important reason why I had one is that I live in a small country town, and I had planned to have the baby in melbourne which is 2 hours from where I live. There is a hospital 25 mins from me but I refuse to go there because of past bad experiences. So for me if I thought something was wrong it wasnt just a quick trip to the hospital to have the heartbeat checked - it was a day trip.
I got mine at about 20 weeks, if I was concerned about bubs, I would drink ice cold water first or lie in a certain position to get bubs moving - I would only use the doppler if I was really concerned. I never had an issue with finding the heartbeat although it did take longer on some occasions.
It is a personal choice but for me it was a good one.