Consumer grade respiratory rate monitors ?

Newer Garmin watches (e.g. Garmin Venu) can now measure respiration rate from wrist based optical sensors and newer Garmin HR chest straps (e.g. Garmin Fenix 6). According to the Trainer Road forum, this seems also to work with the Sosche Rhythm+ heart rate sensors : https://www.trainerroad.com/forum/t/respiratory-rate-from-garmin-hrm/44396/16 and eventually also with the Polar OH1. But are …