Smaller case capacity of the .45 GAP, coupled with higher pressures (you can't get anything for free, as TANSTAAFL!) make reloading the GAP a less forgiving endeavor than the venerable .45 ACP.
Brass is harder to come by, more expensive when you can find it, and case life would be shorter, I would think.
If you were going to try for a complete Glock Collection, sure, jump on it.
TheGolden Rule of Tool Use: "If you don't know what you are doing, DON'T."