Yeah, the time mode options are what makes this effect useful, but the filters are what make it interesting! Rezzy has always had issues. John's been looking into it lately, so I'm hopeful it will improve. I might change the warning window to show for both modes, since they both can be rather unstable as different resonances. By the way, the same flexible filtering options are available is "ShapedUp" too, which makes for a really great distortion effect. If you have any other interesting filter suggestions to add, let me know!
Ping pong seemed to be working for me, but I can take a closer look tonight. I'll point out the obvious just in case, sometimes I miss the simple stuff; make sure the left and right delay times are different, otherwise you won't notice when it changes ears. I do seem to recall that I like to implement my ping pong a little differently than the common way, but honestly it's been so long since I compared my code that I can't recall what I do different. Try turning on ping pong and swap l+r at the same time, I think that might be what you're expecting to hear?