This MCU is being used for some of the new advanced firmwares. The attiny25 SSU is the same physical size as the attiny13a SSU, so it can be utilized on all existing driver layouts.
This driver can only run down to 2.7V, so set your low voltage protection accordingly (you shouldn't need to ever run much lower than that anyways with a single lithium-ion cell).
FIRMWARE PROGRAMMING OPTIONS - FET + 7135 Clicky
ToyKeeper hit this one out of the ballpark! This is similar to the BLF A6 firmware, but with a lot more options. For more information, click this link.
ToyKeeper has been at it again! Crescendo is an awesome clicky ramping firmware with thermal control, among many other awesome features.
For more information about this firmware and user interface, click here. Source code available here.