No I do not believe it is a safe way to carry.
Yes it is less secure.
Good reasons have already been given. In addition drawing from that high of position under a buttoned shirt would be difficult.
I have to disagree. With just a little practice pulling the cover garment with your weak hand, it is not difficult at all to draw from that position, even carried that high. It's actually easier hen the gun is that high, because it allows for a better, quicker grip on the gun.
Even one handed, it's not much trouble drawing, even with a button-down shirt hanging low over the gun. I've got a toddler and carry her on my weak side so my strong hand is free to draw. (God forbid...) Even with a button-down shirt, it's not much trouble.
For some practice/testing, hold a pillow, or box, or bag of groceries in your weak hand, and practice drawing. It doesn't take long to get comfortable with it.
Personally I find it much easier than drawing from 4-5 o'clock position, especially when you when your weak hand is holding something.
My advice, as someone who every-day appendix carries, is try it. Even if it means carrying unloaded around the house to build familiarity. My bet is that in time you will be comfortable with the idea, but will seek out a single-clip holster fe more physical comfort.
Belly pokes, gun falling out, and bending down? No, I doubt it.
Belly pokes happen, but they aren't that frequent. This is another reason for a single-clip holster, so that the rig can twist a little as you move. You also learn to kneel down more instead of bending over too, so that helps with a lot of the typical worries... Also worth noting, is that appendix carry allows for a looser belt, again so the rig can move as needed. He's also carrying a Glock, which doesn't have much of a beaver-tail, so there isn't much to be poking you anyway.
No disrespect, but a lot of the negative comments here make me wonder if these same people have ever carried AIWB, at length before. I have never come close to the gun coming out of the holster when carrying...