Put a set of TFOs on my M&P 40. Rear sights were easy but it took me three days to find the little disk retainer that covers the striker safety spring. The front sights were a bloody nightmare, and although they work, I'm really kicking my butt when I look at the final job. So bad cosmetically that I think I'm going to order another one, and I am no newbie to dovetail installations. But the pistol is WAAY worth the effort.