I understand the desire to drill out consecutive diameters to find the right size hole (esp. as eyes get worse). I put a Lake Compass flip on my LAR-15, because it is shaded, and the peep is actually a tiny plate that can be changed out.
I got the MCARBO replacement for the S2K for a couple of reasons. One was so I could put it up or down at will. The KelTec guys say you could break off a couple of tips on the stock sight, but I’d rather not. If you haven’t seen the MCARBO one, the hole in the peep is beveled, which makes it easier for me to see.
Mostly, I don’t use the sights. Too hard without a stock, as the tube sits too low to get my head over quickly to line them up. I just look over the top of everything toward the target, and at 25 yds., looking at center mass, all of the hits are a fist or so high, and within a fist-size area (your mileage may vary). If I need a head shot (say, in a match stage), the MCARBO peep and Red Lion front work well.