I'm new to the sport and have just ordered a shot gun.  

An acquaintance from church, who has hunted for years, was talking about adding a red dot to his shot gun.

Is this useful?  If so what kind of red dot would be used?  

Thanks

I did it when I converted my Remington 1100 to a makeshift slug gun.  Purchased a
rail mount that attached to the receiver and put a low profile Primary Arms red dot
on it.  It worked OK for slugs out to maybe 75 yards.  I don't see why it wouldn't work
as well or better for centering the shot pattern on a turkey load.

Mount

Primary Arms micro dot

Don't really know how long it would hold up, but I shot 20 or so HV slugs while sighting in
and testing loads for accuracy.  Never had any issues to indicate it wouldn't work.

Burris makes a system that mounts between the stock and the receiver.  It's quite a bit
more expensive, but I can't imagine Burris putting their name on something that doesn't
work 100%

Burris Speedbead

It works really well for turkey, especially if you have a real tight choke and pattern.

Should be good to 60-75 that way.

Certainly will work. Many run optics on their turkey guns - myself included. Really sucks when even Firesights blur out on you.

Thanks guys,

will any old red-dot work?  

A Bushnell TRS-25?

A Sightmark Ultra-short Plus?  

Any quality red dot should work. Some of the cheapos may or may not stand the recoil of a turkey load.

Also, with any of the higher profile sights, you may have to get a cheek riser.

Tagging for recommendations. Right now I'm planning on a TRS-25 on an Aimtech mount on my moss berg 500.

DeltaPoint on my 870