1) You DO actually need a PC to connect. There is a step after you have connected to your wifi that requires you to go to a PC and enter a code at a specified URL. I thought about trying to do it on my phone, but wasn't sure if the process would complete normally or if it needed a device connected to the wifi to navigate to the URL and enter the code.
2) It's free, technically, but to use the Roku for anything you need to register with them, which also includes being required to provide credit card (or PayPal) information when you register. They say this is needed in case you buy premium content, but is sneaky in my opinion for a device that says it's free to use.
3) I guess you should assume that anything free isn't ever going to be good, and Roku is pretty much the same way. When I finally got going with it, there were two limitations that I faced. One is that even though HBOGO could be set up to stream to the Roku, it isn't allowed if you usually connect to HBOGO via a DirectTV account. Seems like I still need my laptop to watch HBOGO. The second limitation was that most of the content was, for lack of a better description, low-grade B-level fringe programming. I have never heard of most of the movies available, and the ones that I had heard of, like Pumpkinhead, were the 5th in the series and not the original movies. I was looking at a screen and had a choice between Pumpkinhead 5, The Fan, and Gladiator (no, not with Russell Crowe).
All in all I'd say that the Roku isn't worth it. I don't know if the features are a lot more than I was able to peruse at the time, if I expected it to be something else, or just don't get the concept of the device, but it just seemed like to me a $50 network adapter card that allows you to watch things that you already have a subscription to on a non-connected TV. For that, however, I already have a laptop and would recommend to others who have laptops and are considering this to not bother; it will likely be found as a waste of money.