Besides BTT I also use another app for Trackpad gestures:
Unfortunately Jitouch is very unstable and only gets an update every 1-2 years. A lot of its gestures are already in BTT, but not all. With Jitouch one can draw lines and letters using the index and ring finger at the same time. I find this really useful and couldn't live without these gestures. They highly increase my productivity!
I would appreciate it a lot if these gestures could be added to BTT.