I had grommets about 15 yrs ago. Absolutely no problems with flying. They come out on their own after a year or so, but the eardrum heals up very quickly. Having had persistent problems with difficulty clearing my ears, the grommets did of course fix that when they were installed, but the effect persisted and I no longer have the problem.
I do recall a brief period of pain as one of them was coming out, but went to see the doc and he extracted it with tweezers (or whatever).