So I now have the E-Werk, and I've had a chance to try it out. With the lights off, my battery indicates that it is charging by 11 mph (it specifies 5V and 1.5 A for input, which is how I have the E-Werk set).

Also, I visited my friend who already has the iPad last night. His iPad indicated that it was at 90% charge, and I was pleasantly surprised to see that it said it was charging once it was connected to the battery. We put it to sleep, and an hour or so later it indicated that it was up to 100% charge. My battery still had ~25% of its charge left (that's a crude estimate based on its status lights).

My battery claims to have a capacity of 10 Wh, whereas the iPad has a 25Wh battery. So, even if the charge transfer were perfectly efficient, it would take 2.5 charging cycles for the battery to fully charge a depleted iPad. However, as I mentioned earlier, my intention is to just use it for an hour or so per day, and I think that should be doable with daily top ups.