what are the advantages of the 'telescope' collapsible stock versus the side folding locking stock?
The collapsible stock came from the factory on my original Mossy, and I found it to be solid, low-profile, and very comfortable under recoil. It has a fairly wide range of adjustment too, and is compact when fully forward.
When deciding on a stock for the new 500, I gave it a LOT of thought. I read with great interest the many excellent comments from very experienced shotgunners here on THR and elsewhere. Many advocate a standard stock on any shotgun, especially with the location of the Mossberg's safety. I took their wisdom very seriously, and considered putting a Speedfeed stock on it. However, after a lot of consideration, I decided on the collapsible due to the things I liked about it and mentioned above, as well as to maintain consistency between both guns, and the fact that my significant other may have to use it, making the adjustability an added plus.
I see the point about how any pistol-grip stock makes the Mossy safety impossible to reach while maintaining one's hand in a true, ready-to-fire position. I found that I can easily operate the safety from a modified position though, and still pull the trigger if necessary. After thinking about the various options, and actions necessary should the SHTF, and given the primary purpose of these guns as home/office defense, the safety isn't a concern, as I decided to maintain them with the safety off, hammer forward (uncocked) and empty chamber. This means all I'd have to do is pump and fire. No need to fool with any small parts like the safety button or action lock while in a stressful situation.