"I don't like gear that fails catastrophically"
I'm generally a fan of Granite Gear; I use their packs exclusively and have had good experiences with the regular non-eVent version of these bags. The eVent style, however, has failed me twice in quick succession; using an 8L bag to hold my Marmot Plasma 30, the bottom eVent panel first frayed then blew out; the replacement Granite Gear sent did the same thing. I like the idea of a breathable bag, but by simply kneeling on a drybag to squeeze the air out, you can accomplish the same result with less chance of structural failure. I'd stick with the regular CTF3 drysacks for safety.
"Still feels too good to be true .. so far, solid ..."
The transparent fabric is wonderful for seeing where stuff is inside. They are light - unbelievable fabric. I haven't gotten really drenched in rain while packs in one of these yet so they haven't met the acid test. On the good side, they've survived several weekend trips without a tear/rip/puncture. Still not trusting them yet - almost too good to be true. Will keep using them and hoping for a frog-drowning rain weekend so I can write a better review.
"Hard to imagine a better drysack for a down sleeping bag"
I've also used the previous Uberlight (w/o eVent) which is also a very fine sack, but this definitely takes things up a notch. Much easier to compress a sleeping bag (with your knee for example) while rolling down the top. Seems just as tough as its predecessor. Great 'insurance' for a $400 sleeping bag in my pack. Haven't tested its waterproof limits - only splashed it with a hose to ensure it could handle an "I'm an idiot" moment with a water bottle or around camp. Expensive, but a great piece of kit if you can afford it.