I tried both. BetterTouchTool does support the no-animation left/right space actions, but on my machine InstantSpaceSwitcher felt a bit snappier for actually moving between spaces, so I kept that for my keyboard shortcuts for previous/next space and direct jumps to a specific desktop. I still use BTT for Mission Control / spaces preview. So for me the final setup is: InstantSpaceSwitcher for fast space switching, BTT only where it still adds something.
that is weird, BTT's space switching should really be instant when used via keyboard shortcuts. (Developer of BTT here)
One advantage of BTT's current implementation is that it still allows you to move windows to the next/previous space while dragging them and simultaneously executing the "Move Left / Right a space" action. In that case there will be an animation but it will at least work.
Your blended setup makes sense.
I like that BTT lets you tune the swipe gesture sensitivity too (Settings → Trackpad → Swipes). I made it more sensitive (0.15) and swiping between Spaces feels very snappy.