has anyone used this and what do you think?

Several of us are using them where I work. So far no malfunctions attributable to rings. None of us have enough rounds on a set to say much at this point.

solution in search of a problem...

at some point in the popularity of the AR15, someone began to perpetuate a myth that if the slots in the gas rings on your bolt lined up, your rifle could short stroke... people began to panic and after every cleaning spend time ensuring that the slots were staggered...

what people failed to realize is that when you put the bolt in the bolt carrier, those rings compress to form a tight seal and those slots close up... this was confirmed by people intentionally lining up the slots and having NO ISSUES whatsoever, in fact there was someone on here who removed 2 of the gas rings and the rifle still worked...

save your money

I agree don't waste your money.

I needed gas rings last year during the Obama craze and those were the only ones I could find. They were way to tight and the rifle became picky about ammo that had functioned in it fine before the install. After tens of thousands of rounds in several rifles I have never had an issue with the rings lining up.

I bought 6 of them only to find differant dimensions from ring to ring. One actually wouldn't let the bolt go into the carrier.
Order this from Bravo;

http://www.bravocompanyusa.com/BCM-Gas-Rings-p/gas%20rings%20set%20of%203.htm

or even better, This;                                                                                                                                                                http://www.bravocompanyusa.com/BCM-SOPMOD-Bolt-Upgrade-Rebuild-Kit-p/bcm%20bolt%20upgrade%20kit.ht

Leave the O ring in your parts box. Install the rest.

i've had great luck with them, i've seen other people post about problems, but have yet to experience problems with mine.

A number of us are trying these rings.
Would you mind sharing some details?
What is your barrel length?
What length gas system?
Why did you think your old rings needed replacing?
Do you know about how many rounds you had on them?
When you say the McFarland ring was too tight did you run a particular test or did the bolt just feel tight pushing it by hand?
Was your BCG or at least the ring lubed?
What do you mean by picky on the ammo?
How did you resolve the issue?

+1000000

Of all the things to worry about this is real close to the bottom of the list.