I think it is a cute way to contect with bubs for dads we bought one off ebay and it was useless (about $50) was always very easy to find Noahs heart rate with a proper doppler but the at home one we never found it! I would consider one of those ones you can hire for about $39 per month i think they are proper ones.

You could consider other way for ur partner to connect like shining a torch on your belly to atract bubs attention or use a bell near your belly for daddy baby play time

also bubs heart rates are round the 120-180 beats per min so much quicker than yours