Ok, I’ve got a chance to pick up a lightly used 229 Legion. I’ve got a bunch of 13 rd mags for my 228, will these function and be reliable? Anyone used them in a 228A1, 229 Legion, or 229R?

Mine work great!

I bought a pile of the 13 rounders used on sale for $7/ea for my 228. Just picked up a 229 and they have yet to fail me. They rattle a little bit. But never had a problem.

Realize you already know this, but posting for anyone that might not know the background on the 229-1 designation and sees this post.

A few years back Sig changed from having two different frames for the 229 (one for .40/.357 guns and a smaller magwell for 9mm). When they switched over to a standardized frame (the .40/.357 frame is now used across all calibers) you saw the 229-1 destination come out for these newer gen 9mm. The Legions, unless I’m wrong, are all 229-1 frames. As such the older mags still work fine, but don’t quite fill up the wider area of the frame where the newer mags flair out.

All that said, yeas they’ll work just fine, but as noted rattle a little due to the loose fit.

I have tons of the old 228/229 mags as well as a bunch of 229-1 mags. I've got guns with both frames.

The 228/229 mags work just fine in the new 229-1 framed guns. And IMO one doesn't rattle anymore than the other. The dimensional differences are negligible. Just enough that the 229-1 mags will not fit in the old style 9mm frame.

I'm the odd duck in this all the time, which I think reflects the failure rate is small. Yes they work. Do they work well enough for serious purposes, NO. I've had issues on some of mine.
Range use I'd be happy.
If they worked perfect I doubt sig would release new mags to fit.
FWIW.