I bought the MagGuts gen-2 +1 kits for both of my Shield carry mags (8 round extended mags) and went to the range today to verify their operation. I couldn't be happier. Not only did I put more than 100 rounds through each mag without any problems whatsoever, loading the mags is actually easier and smoother than when they were stock.

The gen-2 kits are the ones with the zeespring, and you do have to take care when installing that both sides of the spring are inside the follower. If you're not paying attention, it's easy to end up with one side of the spring under the edge of the follower.

I only carry one spare mag, and going from 16 to 18 rounds is significant to me. This was money well spent.