Madbull x ACE Skeleton Stock for M4 Series Airsoft AEG Rifles
(Size: Small)

"If you're looking for a skeleton stock for your m4 this will do the job for you.
Pros:
Lightweight, does not need a buffer tube
Good materials, doesn't look or feel cheap at all
Easy to install (requires a screwdriver as long as the stock however)
Holds a 11.1v lipo okay enough
Tool-less access to battery in stock
Thick rubber pad on back
Foam pad around tube is removable
Built in swivel mount points

Cons:
Taking the back off and on many times has loosened it and now the back has a little wobble.
Needs a long enough rear wire to feed all the way through the tube to be able to plug in batteries if rear wired.
Non-adjustable by nature, make sure you get the right length. I would have preferred the long skeleton stock after using this medium

Overall, I think it's a very good and sturdy stock. It does not have any real advantages over a crane stock other than that it does not quite have wobble that they do have. It definitely can be a pain in the rear attaching if you have rear wiring but this can be offset by making your rear plug removable since it uses the screw and plate and is much longer than a buffer tube. I would recommend it to anyone looking for a skeleton stock look for their m4 if they're willing to possibly modify their rear battery wires.