I have a YLP Unicorn 1.0 that measures out at 102mm - maybe a smidge over 4 inches. Nice LH351 LED with 90 CRI. TIR optic makes a nice smooth hotspot. Button is reasonably well recessed and not too badly placed on the side of the head. There’s a couple of review on BLF (this one: bmengineer is the one that sold me). There used to be a coupon code but I think it expired at the end of 2020.