So here's a question -- apart from capacity (and 10+1 vs. 8+1 isn't that huge), why was Springfield's 4" XD-S never a big seller, and in fact they dropped it from their lineup?
The XD-S isn't a class leader but it's always been popular and reliable as hell. If you put their 8 round extended magazine in it, and lay it next to a new Glock 48, they're dimensionally very similar. I think Glock wins on ergonomics, but then again their new Mod.2 XD-S is very ergonomic.
Was the world just not ready for a slim gun with a 4" slide?
(They've since released their XD-E hammer-fired single stack in both a 4" and a 5" extended slide, but that gun is really a niche market thing -- weirdos like me who still cling to guns, religion and external hammers).