I have a Remora holster for my Sig P229R. It works pretty much as described; I use it primarily for "slob wear" carry, e.g. pajamas around the house in the evening, and also when I change clothes to do yard work or something and I don't want to bother moving my gun belt to grungy clothes.
I have to cinch PJs a little more to provide some pressure, but the holster stays in place pretty well. If you're moving around a lot, it will slide some, but it's a very slow "creep." I've never had it just shift out of place or drop or anything; there's always plenty of warning and opportunity to adjust it.