I was hoping others would have more to offer, but here is what I can tell you (a mixture of experience and club talk and reading):
HopGuard was originally recommended for use 3x over the course of a season; one application in the spring, one in summer, one in fall. Many of us discovered that after the fall use, mite counts continued to climb. The reason is because HopGuard only works on the phoretic (freerunning) mites - it doesn't get the larger population hiding in the cells. As a result, there was a lot of disappointment and some scrambling at the end of this last season (at least by me).
On the plus side, the initial mite drop was incredible! I can, and probably will, use it again to do a "knock back" if at some point over the season I find a hive with a higher than desired mite load. But as a method of getting rid of varroa to the point where the bees can stay healthy -- well, no. At least not while there is a lot of brood present.
HOWEVER, I did notice that in one of the bee mags (sorry, don't remember which one), Dr. Steve Sheppard, from WSU, did say it could be used during the winter months when the brood cycle had slowed or stopped. This makes sense to me because of the above-mentioned issues. I think some folks would be more comfortable putting a few premeasured strips in their hive over the winter rather than trying to mix OA, and the concept is the same -- attack the varroa when they have no place to hide.
Admittedly, I have not read any of the new literature for HopGuard so don't know if they have changed their recommendations for it's use this year. If not, and you are considering using it, I would recommend incorporating it into a larger varroa treatment protocol. Like I said, the initial drop is great, but there are limitations.