I think that Rem factory extensions protrude past the muzzle only if the barrel is 18 inches.
Can't help but think of Payne's shotgun in Stephen Hunter's Point of Impact:He touched the cut-down Remington 1100 in its custom under-shoulder rig beneath his left arm. In the long tube under the barrel there were six double-ought 12-gauge shells. In each shell were nine .32 caliber pellets. He could fire fifty-four bullets in less than three seconds. Got lots of stuff done with that.
Mine is a +2 extension. Did not know that Rem sold +3 ones. Learned something. I have a box of extensions and prefer +1 versions. They don't change balance and give the weapon an unwieldy or awkward handling feeling. Personal experience has been that they can negatively affect reliability. Spring can hang up on juncture of extension and mag tube. The extra pressure from longer spring can distort shells and also can cause shells to jump prematurely past shell latch or interruptor. These events have occurred in my weapons over a 35 year period. When using an extension, loading up a mag tube and then not checking the weapon from time to time may result in a terrible surprise.