I used this to replace the head on an original Surefire M600DF and it's definitely an upgrade. I specifically wanted one that supported both 18650 and CR123As and would fit on the existing Surefire body. That way I can reuse the rest of my existing setup including the light mount, pressure pad, etc. I did test a newer pressure pad and various buttons but it didn't seem to make a noticeable difference within 100 yards.
This was a replacement head for me and it works great!
Works as intended
Pretty much indistinguishable from the competition. Not to say it’s a bad light - it’s actually fantastic but is right there with everything else at the price point. High candela is definitely a trade off so just know what you want. This is an awesome head if it fits your use case.