So I got the filter Monday and installed it. To elaborate on some of the questions I saw here, the inner filter is, as Wolfman said above, a very fine filter. The walls of the filter arent super thick, but the material is very dense, almost like that of those thick paper work towels you can buy in the box, if you know what I mean. You can not see through this stuff. It is clearly designed to catch the smallest of particles that might would escape or otherwise find their way through the outer filter. My only concern after seeing it, and then putting the two filters together was "My god, thats a lot of material for air to pull through, I may starve it for air!" but after install and cranking the tractor, the intake port on the air box seemed to pull just as hard. I did just a basic 'place my hand over the port and measure the suction' test - very scientific, but I was curious.
One post in this thread mentioned that when they change their outer filter the inner filter always looks new. Ive read this elsewhere before as well - that that inner filter will collect very little over time, as the outter filter does seemingly most all the work. This means that when you do change your outer filter, you dont have to worry about exposing the central air intake to a dirty air box. There is a guy here where I live who runs one of the largest Stihl and grasshopper mower dealerships in the south east - He is well respected in the area and knows his stuff, He told me something one day that stuck with me when I was looking at lawn mowers. Regarding the air filter he said to just blow it off with a blower occasionally or something but don't actually remove it to 'tap it out' or 'shake it out'. He services a LOT of mowers, and he was making the point that constantly pulling dirty filters off to clean them can actually do more harm that good as you inevitably get dirt into the engine by removing the filter over and over and exposing the intake. He argued you are better off to just leave the filter on, only taking it off to replace it or to do one good deep clean on it. Having an inner air filter that you may hardly ever have to remove in this case helps prevent this issue. You can pull that outer filter off as much as you want, and ensire that the actual air intake sitting inside the inner filter is never exposed to a dirty air box. Thats worth $15 to me, Id recommend all owners of an L series to get it honestly, I just see no good argument against it.