In Australia you can get 20% and 80% DEET under the Bushman brand (http://www.bushman-repellent.com). Note to moderator - this is not a plug! I don't work for bushman!
DEET is recommended by the Center for Disease Control (CDC), particularly relevant given the zika problem, and some of the 'anti' sentiment is likely to be hype.
I'm not sure what the concentration of army issue repellent is, but like Zuuk we had to be careful with the stuff in the army. Yes, it eats plastic. I think they had to modify rifle butt materials. I'm guessing it was close to 100%.
On the bright side, some rubbed on your neck kept you toasty warm when it was cold on picket duty.
Anything less than 80% was ineffective against tropical mosquitos. It also prevented leeches and ticks climbing up your cuffs.