well i just got done ranting about my boner over GMS on the "best pump supp" thread, but I don't have any experience with glycocyamine.
I would suggest trying out GMS. Even if you don't like it, your only out 4 bucks. (100g = 3.99 at NP). I take 1tsp preworkout and get out-of-this-world pumps. It works out to be 62.5 servings/100g at 1.6g/tsp. not bad for $4.... you might as well try it out, you got nothing to lose.
I love GMS.