Unfortunately I gave my SP40 to a co-worker before I had a chance to try swapping MCUs on it. So I just have ones for the D25 (and some D10) and the H1. It’s too bad because the SP40 is a pretty nice headlamp. I’m not a big fan of the button position (on the end) but that’s minor. Oh, and some of the UI. And the driver, which appears to be current-limiting resistor setup where output continuously drops linearly with voltage.
Based on these images (not mine) the MCU also appears to be a 14-pin PIC. So short a complete driver swap, I’m afraid I’ll leave the SP40 right where it’s at 
Both the D25 and H1 are pretty easy to swap in a new MCU. And the H1 has a nice linear regulator. The D25 is a current-limiting resistor jobber, but that’s expected at this price point I guess. Apologies for derailing a Sofirn thread, but here’s my info on the H1 (and here’s my review of the SP40 and the D25 (not D25S) for fairness/completeness).