On the Gear S3, if the watch is set with Always-On, our watch faces should still be fully visible but slightly darkened. If you are not seeing this behavior, let us know, and we'll investigate it as a bug.
Regarding the battery drain, we are aware of some of these reports and working on optimizations that should alleviate this very soon.
PS: the issue where the Polar m600 is reported instead of the Gear S3 is also know, and will be fixed shortly. Thanks for your report!