Neil, like you I was not interested in drilling any holes in my equipment. I watched a bunch of videos, including one where a lady had a sheet of plexiglass on the back of a hive to show how the vapours seemed to flow once in the hive, and it showed much better distribution when done from the top entrance. Anecdotal evidence from a few keeps I know that have used it seems to corroborate it. I also don't worry too much about closing the hive up for 10 minutes after treatment (same as the others here).
I have never treated in the spring before, this is a first. I know that I have mites and that loads follow the production of brood rearing. My intention this year is to give the brood as much of a head start on the mites as possible, so I am looking more for a big knock down of mite loads this spring. I don't know that we will ever see the elimination of varroa (in my time) so the best way forward is to keep them at bay until our bees learn to develop some form of resistance themselves.