Yup - I have the Burris Fastfire II on the GG&G flat mount. It works really well and I'm very pleased with it. With my eyes, I tend to use the tactical more at 25-75yds than 100yds, but I can reliable hit a fist-sized group from a standing position with the Fastfire II at 100yds. That was mainly what I wanted it for - tactical accuracy at sub-100yd ranges. My eyesight is bad enough that I struggle with the iron sights, and at the least, I am much slower with them than the Fastfire. I get my enjoyment with iron sights shooting my 1892s as I will not use anything but irons with them - ruins the whole feel of a classic style lever gun for me, while the mini's still feel right at home with optics.
In hindsight though, I think I would have gone with the GG&G rail instead of the form-fitted Fastfire mount - just to have more options for the future (although it would have cost a little more). GG&G also now is offering the FastFire III but I have not seen that sight anywhere yet. It does sound like easier adjustments, (the FastFire II is not bad to sight in, but you need a screwdriver to release the locking screws - I have not noticed it drifting much with use though, so I'm not having to adjust it often). I'm thinking of picking a Fastfire III up with the rail mount in the new year to give it a try.