Tim,
With headed 21 gauge brads (slight head pin) the holding power is better than a 23 gauge brad. In many situations they can be substituted for an 18 gauge brad. The nails hold well for the leading edge of casing, larger wood moulding attached to casework like crown or base build ups, heavier panel moulding, base shoe, scotia, etc. With longer nails I have used it to run base cap after doing a test to see how difficult it was to pull off. In most of these situations I would have used and 18 gauge for the additional holding power vs. a 23 gauge which would not be enough. The holes are much easier to touch up than an 18 gauge. I would not feel comfortable fastening wood through sheet rock with this gun unless the walls were very flat, the moulding was light and thin, and it was backed with adhesive. Even then I might think twice.
I own the Cadex. It fires a pin up to 2". I stock them but have yet to use them. I most frequently use 1", 1 3/16", and 1 3/8" nails. The gun runs about $350. Omer makes one and it runs about $250 and fires up to 1 9/16". Senco is supposed to have one coming out soon and EZ Fasten makes one that Woodcraft used to sell at about $150. It's not the ideal tool for every situation but I have found the expense of the tool justified based on the types and finishes of the moulding I install. The added bonus is that the painter likes the smaller holes.
It can also be used to stitch corners without splitting them and most of the other tasks I would usually use a 23 gauge for. The only time I have ever had anything split is when I was doing a test after I got the gun and it split the outside corner of some box store Ultralite MDF base, but to be fair its the only moulding I have ever seen a 23 gauge split and it will split if you look at it funny or if someone is speaking too loudly while you nail it.