Meh, no API for direct access to Bluetooth (they promised for the end of last year on the Pebble Time Kickstarter).
I still use a lot my Pebble because, unlike almost everything else, you can swim and sleep with it (because has enough battery life). But the Samsung Gear Fit 2 does look tempting and is the only non-Pebble that can also do both.
There's libpebble2 which pretty comprehensively covers the basic features if you want to talk to the watch yourself (https://github.com/pebble/libpebble2/) - or is that not what you meant?
I still use a lot my Pebble because, unlike almost everything else, you can swim and sleep with it (because has enough battery life). But the Samsung Gear Fit 2 does look tempting and is the only non-Pebble that can also do both.