Disclaimer: I am a fan of 1911s, and especially the lighter/shorter versions. I will try to be objective, but I readily admit my biases.
As stated above, the Defender will accept the Government-length mags, but will protrude from the frame approx 1/2".
If you do so, you gain one round back, but compromise the concealability of the handgun. You can get 7-round flush-fit Officer mags, but test any mag to ensure reliability.
The shorter 1911s get some bad press...some deserved, some not.
It is a fact that the shorter 1911s have a smaller window within which to operate correctly. The slide is both lighter and shorter, the springs are heavier...everything happens faster.
If you buy a quality small 1911 and keep fresh springs in it, you will likely have no problems.
ETA: if you can, try to see if you can test-fire the pistol you are buying, not only to see that it functions, but especially so you can experience how a 3" alloy 1911 shoots. Enjoy.
Of course, that is true of larger and heavier 1911s as well. That has been my experience, anyway.
I have had...let's see (grabs paper and pencil) to the best of my recollection, nine different 3" 1911s, four with steel frames and the remainder with aluminum alloy frames.
(Also, two Springfield EMPs, which I am excluding from this discussion because they are a 93% scale model of a 1911, and the frame/slide/barrel are not interchangeable with any 1911.)
Bottom line: a 3" 1911 (especially one with an alloy frame) is a very carry-friendly and conceal-able handgun. If you like 1911s, but don't want to carry a +/-38 oz. steel 5 incher, you will very likely love the 24 oz. Defender.
Oh, one more thing. Some people put tons of rounds through their lightweight 1911s. Aluminum is lighter than steel, and will experience faster wear as well.
I shoot my carry guns, but I don't use them as range guns. I have a steel 1911 that I put a good number of rounds through. I put a few mags through the alloy framed model to insure that I can still hit what I am pointing at. This way, the steel 1911 gets the majority of the range rounds, and I shoot the alloy one enough to be confident in carrying it.
I used the same tactic when I carried j-frames. Try to wear out the steel one (not bloody likely), carry the Scandium one and shoot it a bit.
