I have the 20" one for AA flashlights.

I put it in the breech and look in the muzzle with a magnifying glass.

I can see:
1) if there is any Copper fouling in the last few inches of bore
2) if the barrel was lapped at the factory
3) if there are chatter marks from when the button was pulled through the bore

http://www.niteize.com/product..._id=28&product_id=68


I recently got the LED upgrades for the flashlights.

The AA and AAA flashlights LED upgrade regulates LED current with battery impedance. $5

The C and D cell LED upgrades have an electronic pulse width modulation current regulator. $15

Good info!
Thanx for posting about it.
I will look into buying it...

Don

Thanks for the info. I just ordered one. For 7 bucks I figured what the heck