rear firing tweeters....

I do like that the Von Schweikert rear firing tweeters on the VR-4 and other models have attenuators so that you can adjust the level to better integrate the speaker in your listening space (or your listening preferences).

My satellites have rear-firing tweeters as well as the front ones. It certainly adds to the spacial qualities of the speaker system, but the stated goal of the designer is to even out the in-room high frequency response.

I had those Snells. E-IV, I believe? I liked them, but not necessarily because of the ambience tweeters. I think they were just good, high-value speakers.

To me, it seems a rear-firing tweeter is basically a reverb unit. There will be some delayed arrival at the ears, delayed enough to not cause phasing errors, but perceived more as an "echo". Ultimately, I'm not really comfortable with intentionally smearing the HF response in time to add "ambiance" beyond what is captured on the recording (or not).

The goal, at least for the Revels, is to smooth the polar response.

Sonus Faber seems to like the idea.