We tested a lot of ECG devices integrated with our iotool.io smartphone IOT gateway. Results:
1. Zephyr BioHarness3 - supported readings: best all rounder, 1 lead, textile electrodes or medical patch, other sensors, like activity, very reliable, decent battery life, offline download to PC, Bluetooth, sends data directly to iotool.io smartphone gateway. They also have an FDA approved device. We are using it in several healthcare pilot projects (like patients with CHF) and first responders. USA product.
2. Faros Mega - similar as Zephyr, sends data directly to iotool.io smartphone gateway, The main difference: sampling frequency is lower, battery life is better because it uses BT LE, up to three channels. EU product
3. Shimmer research ECG, more "researcher's" oriented, only ECG, EU product
4. VitalConnect HealthPatchMD, disposable battery and patch, USA product
5. Other up to 12 lead ECG, like INeedMD (nice concept!) or Shiller - but they are made for more "hospital" or "niche" markets
We use all of that sensors on the field, so do not hesitate to contact me directly in case of any question