We purchased this product after suffering a missed miscarriage. Upon conceiving again, my wife was finding it extremely difficult to relax and enjoy the pregnancy. We invested in the Doppler in the hopes that we would be able to pick up the baby's heart beat whenever we needed a bit of reassurance. The machine has never disappointed us. From the first day we received it at about 13 weeks of pregnancy, we have been able to pick up our baby's heart beat. We find all the other sounds comforting too. I would caution that should the baby be hiding, then a lack of heart beat could be distressing, but this has never been a problem for us. Do have patience though, as the end of the probe has to be tilted in the exact direction of the baby's heart to work properly. Sometimes even a fraction of a millimeter movement in any direction can pick the little one up. Also be aware of which heart beat belongs to the baby, as the machine does pick up your own pulse as well.
The baby will beat at between 120 and 160 ish and sounds more like horses galloping. It is worth the extra few pounds to get the machine with the digital display as you can be more certain you are infact listening to your baby.
Overall, this is the best money we have spent so far this pregnancy. You can't put a price on peace of mind.