I'm using CrossBreed appendix holster, and it's been a great choice. It's comfortable, easy to draw from, and stays in place even when I'm moving around a lot.
I chose a smaller holster maker that focuses on molding for the P226 series, and I’ve found it surprisingly comfortable for daily carry. The MK25 might not be as easy to appendix-carry as a slim striker gun, but with the right holster, it’s definitely possible.
I use Tier 1 Concealed Axis Elite. It’s built tough, feels great to wear, and the dual-clip design keeps my gun stable without any fuss. The appendix carry can be a bit tricky with a full-size SIG, but the Axis spreads out the footprint just enough to make it work.