Got mine yesterday too. I've been playing in FroYo land so I haven't done much other than charge them up.
Here is the specific kit I have. This link shouldn't expire
HTC EVO 4G SPRINT HERO 2x1800 mAh Battery Dock USB items - Get great deals on items on eBay.com!
The build quality of the charger is really poor. Not falling apart or anything, just cheap materials. The charger does work and the charge indicator light is kinda nice. I've topped off the stock HTC battery and the Seidio "3500 mAh" with it. The Evo shows them at 100% when I put them back in, so I'm guessing this is a good sign.
The batteries have rounded sides instead of the squared shape of the stock EVO battery. This makes them a little off-putting when removing them. You can get it our with your fingers, but I just pop the phone into my palm to take them out.
I don't have a scale, but the batteries feel a bit heaver than the stock one. This would be expected if these things are really 1800 mAh.
As for life, they work and I'm seeing longer life, but like I said earlier I've been dorking around with FroYo. I'm not sure which is helping.
The increased life isn't anything groundbreaking, but I'm almost comfortable enough to say they perform as well as the stock batteries.
If this holds true, this is a good deal. Two batteries and a charger for $30 shipped is really decent.
That said, I didn't think the battery purchase through too well. I carry my phone in my front pocket and these little cells store a bunch of energy. If the manufacturer cut corners, as many no-brand Chinese companies do, I'm not terribly sure I'd want a potential explosion that close to my man-junk.
I'll be watching the batteries very closely