If you use apple products all time then you will have no trouble at all navigating around the app. If you don't then it's quite easy to use, once you get the gist of it. The app only has 3 tabs (sections): On Now, TV guide & Settings. You can have multiple HDHomeruns on the network and it picks them all up. My kids have no trouble using it & the in-laws have used it without any issues.
IMHO, I think it's the best app for HDHomerun for Apple products by far. Another reason I like the app is that it's also supported on iOS and not many (good) apps are made for the HDHomerun on iOS.
I've had this app since it was released a bit over a year ago now & it pretty much was the missing link I was after for ATV with the ability to watch live TV, along side of Infuse app for my movies.
In regards to purchasing an HDHomerun Connect (HDHR4), I'd be combing Gumtree & eBay to see if you can pick one up on the cheap. I picked up my 2nd HDHR4 for $90 off Gumtree. Alternatively, check out Amazon.co.uk, I've seen them on special a few times for $150 including postage.