Well built.... Excellent finish.... Perfect fit.....
This extension works perfectly however you will have to do a very small amount of gunsmithing to the shotgun's magazine tube if you have a newer Remington 870. The new 870 has a spring retaining plug which you turn 90 degrees to lock in place. There are two nipples in the shotgun's magazine tube to accomodate this plug and keep it in place. They are deep enough that the rim of a shotgun shell will not pass through. I had to take a Dremel and a round sand paper grinding bit and grind these nipples away so the shells will move past them. It took all of about 3 minutes, including removing all the grindings from the tube. Once these two nipples were removed the shotgun loaded perfectly. This is something you would have to do with ANY magazine extension, not just this one.
For someone like myself (an accomplished do-it-yourselfer) this installation was not difficult. You will need the dremel tool with a good grinding attachment if you want to do it right. A half round file will work but is tedious to say the least! Once the modification is done it works well. Be sure to slick the inside surface of the original magazine or the follower won't pass by the spot where you ground off the tabs