I'm a very satisfied NeTV1 hobbyist/enthusiast so my feedback is based on my personal experience. I've not used my NeTV1 for a large deployment like what you're considering.
Realistically, you should probably wait until the NeTV2 units are available (I don't know when that will be) because the NeTV1 firmware is no longer maintained. Out of the box, your network connectivity on the NeTV1 is limited to wifi, which has some reliability problems, or via ethernet-over-USB where the current firmware is limited to one NeTV1 per computer (think 10,000 Raspberry Pi's, for example, each with an NeTV1 unit attached). If you have experience with embedded Linux you could customize the NeTV1 firmware however you need to; it is 100% open.
2. Adafruit is the official (and only, as far as I know) distributor and at the time I'm writing this there are 19 units left for purchase.