When I was involved with a Girl Scout summer camp a few years ago - we would get the precooked taco meat - not from GFS - but a food supplier was located near the camp. (If any one knows Girl Scouts - all meat coming in to any function MUST be precooked - which is why we did not cook ground beef and add taco seasonings.)
Again - we used a different brand - so YMMV. If you have other great fixin's to put on the tacos - sour cream, guac, a great salsa, olives, onions, tomatoes - the whole 9-yards - I think this will be fine. (If you are just doing tacos with cheese and lettuce - that might be a different story)
For a HS grad party trust me - you'll be busy enough, so if this saves you some money, and helps out with the amount of work you need to do - I say go for it!
Is there any way you could buy 1 pack of it - and have it for dinner, and if you like it - get more before the sale ends?