How about this one - Hits are easier to get rid of off of a smooth tank rather than a bottle cover?
With turf at tournaments a tank cover isnt needed so much to protect the tank as it was in the past. And with turf, when you are sliding or crawling quickly, tank covers 'drag' on the turf slowing you down, or causing the tank in face affect that we all cringe to see.
Sports tape or deck tape works well for a little grip. I still prefer my tank cover though