astrialis anything that can connect to gadgetbridge. Some devices are more compatible than others, and some require to first use an official app to capture pairing token. From what I've seen, Huawei devices have decent support and no need for tokens. They are also relatively accurate.
There caveats with gadgetbridge: it was born as a pebble companion app, and it shows in some parts: activities are recorded based on step frequency, and in general it is mostly step centered, and doesn't do any kind of analysis on data. Also, since it doesn't connect to the network, it can't obtain agps constellation prediction data for the smartwatch. If your main goal is capturing heart rate and step data, export it and analyze it externally, it will be very good for that.