I joined it several years ago. I have yet to use a coupon. You will need to use your coupons and not hold on to them for a long time if you joined at 2 year membership. I did the 5 year so each coupon does not expire until 2020. That said, I don't know how they determine how long your coupon is good for until it will expire. I know I first joined for a year, then after gaining understanding, I went back and picked up 5 more years. So, since I first became a member in 2014, adding the five years makes them good until mid 2020.
Moral, watch the expiration date on the coupons. I've been lazy and have not wanted to drive 120 miles round trip to use one. And I avoid buying my Glocks in my state due to sales tax. That cost more than shipping and FFL combined on a new pistol, usually, in my case.....
The Glock Dist that accepts the coupon is in my state (GT Dist). So, 120 mile drive, sales tax (no FFL since their selling the firearm) equals, me lazy because my saving are not really big enough to motivate me under those circumstances . I usually shop around, and find the best deal I can out of state and usually 20-25 shipping (but I look for the ones with free shipping) + 15 (my FFL fee) so, it is what it is.