The core version also fits S2's, it's not really a metric/imperial thing, just the location of the slot and holes. Whether the core version fits SE's, I'm not sure, but at least as of the SE's I've tried in the last few years, I think it's a different switch, just based on the way the action feels when using it.
FWIW, I had a 3-way blade switch go kaput on me in an S2, and replaced with the core version (only option at the time) and I actually prefer the way the S2 switch felt when cycling it. Which is a completely ridiculous thing to care about, but it's true.