Good idea but poorly executed. This is not a drop in modification. First the spring is too wide and causes the follower to rise very slowly, rapid fire would undoubtedly jam, second the ridge between the original mag and the extension causes the nose of the follower to get stuck there and no more rounds will feed. It took a few hours of grinding down the mag base to get rid of the seam and thin out every turn or the spring with channel locks to get it to run smooth. After much messing around it is working reliably. Kriss' tech support was non existent, the same problem with companies that get some success, they forget that the customers are the reason for their success. Instead of addressing the issue they assumed I was doing something wrong or the original mag was defective. I'm posting this as a warning to anyone who may be thinking of getting one of these kits, you in for more than you think. Is it worth it? Maybe. Would I do it again? Not sure at this point.