I have a 23 and 27. Extensions are not used on my 27.
Both are easily concealable but given the shorter grip of the 27, it is indeed easier to hide. Necessary? No. Would be nice? Oh, yeah! Try a Crossbreed Supertuck or Shielded Holster then decide if the smaller platform is necessary. My holsters and G23 mags are interchangeable. That is a big expense that people do not take into account.
I have done the same with my Kimber Pro (4.25" barrel) Raptor II and my Kimber Ultra (3" barrel) Raptor II. Necessary? No. Would be nice? Yes! The Ultra can fit in my pockets (khakis) whereas the 27 cannot.
Lastly, bear in mind that shorter guns have a shorter sight radius, lower capacity and are a little more in recoil, in general.