I have the PDAir case.
The good: holds phone solidly closed, you can easily remove the phone to change batteries or use a GameGripper, and it doesn't interfere with the keyboard at all.
The bad: the aluminum is kind of slippery, and the metal case noticeably attenuates wi-fi and wimax. It affects 3G, bluetooth, and gps a little, but it *really* hurts 4G and wi-fi. The horizontal bar across the top of the screen makes pulldown notifications a pain to deal with, but that's frankly the least of its problems (and one I personally dealt with by filing away the center part).
The awful: I'm not sure whether it's the electrically-conductive aluminum coming into contact with my grounded body, the foam padding (that seems to be antistatic conductive foam) on the inside, or both, but I have horrible problems with cat hair triggering phantom touchscreen presses, particularly the 'back' button.
The signal attenuation annoys me, but it's the phantom presses that make me keep throwing the case back in the drawer in frustration and going back to my ActiveX (which itself gets thrown into the drawer after I get frustrated by the way it makes the camera button dysfunctional and limits my use by making the battery such a pain to change.
A few weeks ago, I tried painting the case with Plasti-Dip. It made the case nicer to hold, but had no noticeable effect on the phantom keypresses (I thought the insulating effect would solve them for me), and the Plasti-Dip itself all peeled off within a matter of days (if I decide to redo it, I'm going to have to bite the bullet and buy a quart of their primer, which apparently will solve the problem completely, but is impossible to buy offline and costs about $30 online with shipping). As an alternative to the primer, I might try removing the hinge pin, scraping out the foam, and just dip-coating the whole thing (which would keep it from peeling off by transforming it into a solid coating that completely encases the metal, instead of just rubberized paint clinging to a slippery surface.
I personally suggested that they basically tweak the design to eliminate much of the rear metal (let's be honest, if I had to choose between signal attenuation and a 99-cent replacement back from eBay, I'll risk having to buy a new back), cut an access notch into the mid-center of the top (to allow pulling down the notification bar), eliminate the interior foam, and literally dip-coat them with Plasti-Dip at the factory as part of the manufacturing process. Assuming that fixed the problem with stray capacitive triggering, it would make the case just about perfect by eliminating its other problems as well.
With a little extra work, they could even pair it with a new back designed to fit a Yoobao extended battery that maintains the original back's form-factor everywhere besides the pregnant battery lump projecting squarely from the rear, and cut a slightly larger square hole into the lower half of the case's back to allow the battery bulge to project through the hole.
Anyway... do I recommend the case in its present form? Maybe. If ~$30 is no big deal to you, definitely give it a shot. You might get lucky and not have the false-firing touchscreen problem I do. If you think the case is really expensive, and you're agonizing over it... probably not. It's frustrating, because this case creatively solves several fundamental problems that other Epic cases have, but unfortunately introduces a few brand new ones of its own that might or might not be more annoying overall than the ones it solves.