Best 870 Mag Extension? help

[ramair6speed]

So im planing to buy a mag extension for my 870 and theres alot of em out there. Im looking to cut down my extra barrel to about 20 or 18 inches give or take id like for the mag tube to be even or shorter than the barrel. I really want to get as many extra rounds as possible at least three more. Any one have any experience with this would be great thanks!

 

[ATLEMT]

Factory Remington or scattergun technology

 

[renault314]

i have an 870 and an 1100 and i have an ati extension that works for both. I had to file down the tabs inside the mag tube to make it work, but that was no big deal. i didnt want to mod my 870 any more than that so i bought the 1100 to turn into a 3gun comp shotty. with the extender on i can hold 8. i cut about 4 inches off the 1100's barrel and it still hangs over the end by about 4 inches. the extender is 8 inches and my barrell is 24. so from the reciever to the end of the extender is 20 inches. but thats on the 1100, dont know if the reciever and extension would still be 20 inches on the 870. i only spent $35 on mine and love it. the guns run great with them. no need to go expensive, unless you just have to have one made out of aluminum, the ATI ones are plastic. I would buy it again.