It has been 2 months now since I have ordered the cheaper heart rate sensor and unfortunately it got lost on its way here. Additionally I ordered around the Chinese National Day and I lost track of the time so now I'm overdue on my buyer protection. So I'm hoping that they will resend the sensor as soon as they read my reply today.
Some thoughts on the software, I think it will be a good idea to measure the time between pulses and send the value over the NRF24L01s and not the value of the analog read outs. Some what a bicycle computer for your heart. While writing that I just thought of connecting this project with the Open-Bicycle-Computer. Let's monitor the pulse of the bikes rotation and show the heart rate on the bicycle computer!
I'm going to order another heart rate sensor from a different seller to make sure I get one.