I tend to agree, looks really mean nothing to me as far as a block is concerned. I look at my monitor when I am using my PC, not my waterblock. I don't think I would ever be comfortable with any type of a clear top, O-ring setup, especially with non-metallic barbs. Just too risky. Even if only 1 in 1,000 fail, I do not want to be the 1. CPU blocks almost always are directly above very, very expensive video cards. Leaky CPU block=ruined video card. I'll take a solid copper, soldered top.
Check out this guy's nightmare to see what I mean.