Well i use sks for my keys and they are jma ones, it doesnt really matter whch ones you use as long as like you say you know which ones are right.
There are key blank comparison books and although i dont own one i believe the one sold by sks is a very good one, its like a yellow pages
To me it doesnt matter if they are original blanks or not and neither do the customer care, a key is a key its only if they are renown for being weak metal ithat you should stay away from them but the main brands are all ok and its down to choice.