Recently I was seriously considering their course. Three things stopped me:
1) The full course is ~$10,000. Yeah, they have stepping stone levels, and you could try doing it piecemeal. But to get everything you really want & need, it's around $10,000.
2) And that's just the videos. Without another $10,000 in firearms to work on you won't actually learn anything. Seriously, $10,000. I made a list - AK parts kits, AR parts kits, 1911 parts kits, Glock parts kits, a bunch of other stuff.
3) That's a $20,000 investment so you can putter around your garrage and maybe make $100-$200 a week working nights & weekends. Maybe you can afford to drop $20,000 on a hobby. Some people can. I wish I could, but I can't.
Seriously, I ran the numbers every way I could think of. This isn't a knock on AGI. The stuff of theirs that I saw was decent. But to do it as anything other than a hobby just isn't realistic (unless there's a 'smith in your area willing to take you in).
So if you've got a big pile of money, and your only options are either set it all on fire or spend it on becoming a gunsmith, then go for it. If you're thinking of making it a career then give it a lot of thought.