They make the Provari look nicer when you have a tank with a larger diameter than the top taper. The top taper is ~19mm, so if you have 19mm tanks they look good without the ring. The body of the Provari is ~22mm, so for a seamless look the ring covers the taper & makes the body flow right into the sides of a larger, 22mm tank. The rings are for nothing more than cosmetics.
Edit: Others haven't had the same problem, but my first order with Loki will likely be my last. I just got my rings today & they look good, but the shipping time was horrible at best. There had to have been a fluke somewhere along the line since Lion ordered his the same time I did & got his days ago... even though he lives thousands of miles further away from them than I do. 2 day shipping turned into 2 week shipping. Not convinced this was all the fault of the idiots at USPS, but perhaps.
I am not sure it is fair to blame Loki...but then again, you are not known for just placement of blame, eh?
I love my Loki rings. One thing about them, I had to make a minor adjustment to my KFL bottom screw to make the contact on the ProVari with my KFL original. With my KFL-plus, for whatever reason, it was a non-issue. With my IGO-T and IGO-L, it was a non-issue. I have adjusted my KFLs so that the bottom screw is aligned with the air intake hole on the side, and that could be part of the reason I had to adjust again, but be aware of this. The Loki rings are thicker (no gap, fits snug) which I like and am happy to make the adjustment for the tight fit.
I like them better than the Tatroe Rings. Well worth the extra five bucks. Here they are, two brushed stainless and one black delrin. I also ordered the black 9mm hollow point bullet drip tip, pictured here on the IGO-T.