The first one I tried was the version with the ridges on the sides and cutouts for the buttons which seems to be found pretty commonly on ebay (not the version with the buttons built into the case which also can be found ebay).
The finish of the case is very nice, there aren't any rough spots in the aluminum save for a sharp corner at the cutout for the stylus. I believe that the aluminum is anodized, and so the color seems very durable and resistant to normal wear. The phone has no problem fitting inside the case, and even with a SGP Ultra Crystal screen protector, the front piece slides over without issue. There are slightly thick strips of tape that act as bumpers to prevent the case from scratching up the bezel of the phone.
The cutouts, while executed well enough, did not seem to be thought out well and are the source of my complaints. The cutout for the headphones is rectangular, which was weird off the bat. With the phone seated, the plug is lined up with an edge of the cutout, making it impossible to plug in the factory headphones, which already has a very thin plug. The cutout for the micro USB port barely allows the factory USB cable to be plugged in. There is some play with the thick strips of tape, so the phone can be manipulated to allow the plug to fit, but it is forced to sit at an angle. Given how thin the factory USB plug housing is, no other USB cable I've tried will fit properly. The button cutouts are generous at least, and do not hinder normal use very much.
I should note that the ridges on the side of the case do not provide any added grip to the phone, and in fact have made the phone feel more slippery in my hand and when trying to retrieve it from my pocket.
The next one I tried was branded "Zomgo" and was ordered from ebay:
Again, this case appeared to be very well finished. There don't seem to be any flaws in the machining or anodizing. The interior of the case has thicker foam strips, which appear to be much more substantial than the first case. Because of this, the phone fits very snug in the case, and also has a bit more play if forced to move inside the case.
The cutouts in the case again are well executed, but not well thought out. The headphone jack cutout is round, and was the only cutout (aside from the microphone cutouts) that worked properly using the factory headphones. The main problem is the USB port cutout. Although it appears to have a more generous cutout than the previous case, the plug cannot fit properly without manipulating the phone inside the case. The foam provides play and the plug can be forced in, but it also sits at an angle like the first case. Although in both cases, the plug can fully seat this way, it does not seem ideal and may damage the plug or port. That said, both cases will most likely not work at all with any other USB plugs that have thicker housings than the factory one. The cutouts for the buttons are smaller and deeper than the first case, causing more difficulty in accessing the buttons.
It should be noted that both of these cases offer no type of rear protection when laying the phone on the table. Most of the back cover actually sits further out than the edge of the case, and so I've gotten in the habit of laying the phone face down to take advantage of the lip on the front.
I will attempt to fix the second case by removing the thicker foam strips and replacing it with something thinner like the tape inside the first case or similar (possibly electrical tape). Hopefully this will allow the phone to be positioned inside the case where the USB port lines up properly with the case cutout.