The battery arrived a little while ago, and here's my initial impression:
First of all, it's definitely not as sturdy as an OEM battery. The bottom cover shows "waves" indicating the structure underneath, where OEM battery looks to be either a solid piece of metal or plastic and has no perceptible give or distortion. The charge level button is also molded into the bottom cover, rather than being a separate piece as on an OEM battery. The color is close if not identical to the OEM battery.
Mine arrived with about 25% charge. The LEDs on the bottom indicated this, and the system confirmed once I'd started it up.
The biggest downside I see so far is that it's a very tight fit in the battery compartment. It took a fair bit of pressure to get it fully seated and retained, and then get the system to recognize it.
I now have it charging. My plan is to charge it fully, and then use the system this evening for normal "light" tasks(web browsing, etc) to see how long the battery lasts.
One small area of concern is that System Report shows it as having a "full charge" capacity of 3985 mAH, and not the 5200 advertised. I'm going to give the system a couple of cycles to get acclimated to the battery before I I take this number too seriously, though.
I'll update once I've run it through a full charge-discharge cycle.