Not required although I use them.

I believe that type AC does require use of the bushings ("sleeves") at terminations -- at least the 2008 Code -- NEC 320.40.

Here is a link that might be useful: Illustration of 320.40

Guess I should have asked AC or MC. MC doesn't require it. I guess because of the insulated ground?

I thought the purpose of the 'red devils' was to keep the insulation on the wires from being nicked/cut by the jagged edges of the metal sheathing where it has been cut to length on the job.
Is MC manufactured that differently than AC?

That Illustrated NEC Guide looks really helpful.

Wish it weren't $70.

What is the difference between MC and AC - - MC = metal conduit? AC ?

Armored cable uses the metal sheath as the equipment grounding with a built in bonding jumper and mc metal clad has an insulated grounding conductor. Using the proper connectors for mc the conductors are held straight away from the jacket. But like I said I still use the red bushings regardless. Looks cleaner. I was on a job once where the contractor sent a note in the checks that they weren't needed and to send them back to the shop. That produced a good laugh.

"Using the proper connectors for mc the conductors are held straight away from the jacket."

This.

The MC clamp has a smaller diameter exit for the wires, and does not allow them to rub against the cut ends of the armor.

It is a much newer design, and eliminates the need for the red anti-short bushings.
It is a nice advantage since a lot of MC is used in commercial work.
The run grounding conductor is also a better solution than trying to use the armor itself and the bonding strip that is needed for a low impedance ground connection.

I rarely use AC but go through a decent amount of MC for both commercial and residential work.
Only having one type available eliminates the chance of using the wrong clamp.

I've only seen AC used once and surprisingly it was recently. Must have gotten a deal or something? I know you save a conductor, but is it worth it knowing one failed connection and you loose your ground?

"... is it worth it knowing one failed connection and you loose your ground?"

No worse than many other methods.
Metallic conduit in many of its guises can be used as a ground also.

The set screw on an AC box connector makes a good connection to the armor, and the bonding strip ensures a connection despite the multiple loops and joints in the armor.

The MC with a run ground can allow isolated grounds when they are needed, but that extra wire costs $.

There is also smooth welded MC that is not spiral wrapped but uses aluminum tube for the armor and has a very small cross section for the cable when space is at a premium. Barely more than 1/4 inch for a 14/2 cable.