Varillas plays fearless tennis. I've seen him play a few times already (on streams or TV), mostly challengers. About two or three years ago, he started to sweep the clay south american challengers. He jumped from outside #400 to inside #150 in a couple of months. It seemed he would keep climbing and reach at least around #50, but as with a lot of other up and comers from this part of the world, he stalled from some reason. He also was not playing that much for a while, but I just checked his ranking history and basically kept inside the #150 ever since. I watched parts of his match against RBA, still the same player, very aggressive. Who knows if the next jump is not happening right now...
He will give much more of a fight than people think. I had him beating HH in my bracket at first, but later on went for the safer pick... chicken shit.
Ofner is a good player, I have seen him play twice. Both times I had the feeling he should be ranked higher than he is (but rankings don't lie...).