What does everyone think of the 9 mm gaurd dog ammo?

Junk

Better than FMJ but not by much. At least it's an option in locales where JHP's are prohibited or for older pistols that won't feed JHP's.
Tomac

Invaluable in the situations that Tomac listed.

Look for EFMJ's instead. Same concept, but you should be able to find some in heavier bullet weights and in 50rd boxes. ...That is 'if' you can find it of course.
And if you have the option, go for HST hollow points.

I've always heard the Guard Dog ammo worked extremely well, so well it was recommend even for use in areas where other ammo was legal.  The concept is great but I've not seen any tests done, just people saying they witnessed a test and offering up their opinion based on that.  The idea of a home defense ammo that penetrates, expands and dumps its full energy into a bad guy with little to no risk of over penetration.  People today have been brainwashed by the internet into thinking if you aren't using the hottest ammo available used by the FBI and MiB then its not going to work.  Same thing with hunting the internet generation swears you need a .454 Casull for black bear and a .375 H&H for brownies, hell most people think hunting feral hogs with anything smaller than a .308 is pointless because the bullets will just bounce off.  I'm more inclined to believe the Guard Dog ammo works as advertised instead of the other way around.

TEST

Probably ok in the scenarios listed. Great for their designed purpose with family members or neighbors on the other side of walls. As a carry ammo I have really been impressed with the tests of Hornady Critical Duty. That is what I have switched to for winter carry. I still trust Gold Dot's 110% in the warmer months.