I first started using the Mesa Tactical side saddle about 6 months ago. Since then, the gun and the carrier have seen a lot of time on the range. Most recently, the Mossberg 500 was used by another shooter in a one day defensive shotgun course. The Mesa Tactical shell carrier worked flawlessly, as would probably be expected. One other shooter in the class was also running a Mesa Tactical side saddle on an 870 and had similarly flawless performance.
I have been very impressed with the build quality and functionality of the shell carrier, plus it is the only 8 round shell carrier I could find. The only critique I would have is that if it is left loaded for an extended period of time, the polymer inserts that retain the shells to start to take a set and shells are not held as tightly as I would like. If the shells are removed for a day or two the issue remedies itself, but it is still a hassle to deal with, especially if the shotgun is used in a home defense or duty role and needs to be ready at a moments notice.