Not sure why people complain about the invite system, it's pretty easy to get one, I just jumped on the public offering in october, and got one easy. For the money, it's not a bad phone, but it's not a great as it's cracked up to be, there is a reason why it's cheap. I (And several others according to the forum) have had issues with the screen. It sort of flickers a little sometimes, a reboot fixes that. The screen is also sometimes hard to read in bright conditions compared to what I'm used to. Also the lag/misinterpretation of the touchscreen as described in this article, is VERY annoying.
Another thing. As some mention, the specs are not stellar anymore, this is already an old phone, and compared to the iPhone 6 Plus it feels old. The old saying is you get what you pay for. Well with the One, you might get a little more than you paid for, but it's not so much that it rivals the new flagship phones.
If you decide to get one, get a screen protector. The screen is very brittle, and when it breaks, it's almost certain doom for the phone. The glass shatters in a way Corning Gorilla Glass would never do, and it also most often destroys the functionality of the screen. Reading through the forum, comparing to how many have actually bought one, there are surprisingly many cases of smashed screens. A drop of 1 feet (On hard surfaces), has destroyed quite a few Ones. And the RMA is a nightmare. It takes forever to get it fixed, and the screens are a lot more expensive that getting a Note 4 or iPhone fixed, factoring in transport etc.