I considered this a few months ago. I have never shot it, but I did quite a bit of research and, all things considered, I didn't do it.
First, it's $699 (if I remember correctly). That's a lot of money. That's a whole new Glock plus accessories/ammo.
In addition, the 50 GI seems like it's basically for bragging rights; a big hole on the business end. It offers ballistics between a .45 acp and the 10mm, has an 8 round capacity with Guncrafter Industry's magazines (7 less than 10mm), and when I was searching for ammo I had a pretty tough time coming across it (may be more available now).
Finally, in connection with the ballistics statement above, it is just not what I thought when I heard of a .50 caliber bullet that I could shoot through my Glock. It is not the .50 AE that the Desert Eagle shoots, and if that's what you were expecting then you will be disappointed.
I'm sure it would be adequate as a self-defense round. It would make quite a large hole, but for $699 you can buy literally hundreds of rounds of the best 10mm defense ammo on the market, get plenty of practice shooting it, and it would likely provide better defensive capabilities (or at least equal).