I take no responsibility for any issues to your watch, your house, your job, your kitten, blah blah.
It's recommended to boot it via "fastboot boot twrp_swift_*.img".
To flash, use the default "fastboot flash recovery twrp_swift_*.img". To boot into recovery, use adb or hold center and bottom button when off. Everything is tested to work fine.
If you want to return to stock recovery, flash recovery image from here.[/SIZE]
Recommended platform manifest
Thanks a lot to @joeykrim and @T10NAZ, I used their Zenwatch 2 thread as a guide to compile the kernel and recovery.