I thought you were supposed to use Siglo on the Linux desktop as the companion app? Might be worth a look if you haven't checked it out yet.
I have to say, as much as I like gadgetbridge I'm kind of jealous of InfiniLink on iOS.
As for software, I use the BPM vibration feature to time static stretches (set to 1 pulse at 60bpm). Means you don't need to keep count in your head to (accurately) get that minimum 28 second static stretch time, nor do you need to crane your neck and look at a clock as you're doing them. I only wish it saved the bpm config so you didn't have to manually define it every time you use the feature, since it's kinda finicky to operate.
Good find, I don't have an iPhone to play around with it, but it looks very slick, and seems to be a first party FOSS app for the watch. Hopefully they get that missing functionality in the future.
In the case of Android, I'm not actually sure if you need gadgetbridge running for all of the above functionality. I should try unpairing and reconnecting with GB disabled or uninstalled to verify.