I will admit I am impressed with the quality of the picture, dare I say it is better than what my cable picture gives me. I had forgotten how many commercials were on TV.There's a start button? Or do you mean the menu button? I don't think I've ever used the button on the left side of the xbox button.
I'm using the Sling app for my free month anyway, and it seems to work fairly well. It takes it a bit to initially load and if the menu guide doesn't load beneath the channels, you have to exit the app, kill it with the menu button and restart. It seems if it doesn't "sync" on the initial boot, then it never does and you'll never be able to tell what is currently playing.
The video quality is great after the initial blurry buffer that lasts a few seconds and I've only had one live buffer delay while watching a program. I haven't tried using it on anything other than the Xb1 though, so I don't know how it interacts with smartglass or anything else.
The one issue that was really annoying me turns out not to be a function of the Sling app, but of the Xb1 - closed captioning. There's a couple universal settings for closed captioning that are in the console settings.
Once I got that sorted, it was pretty good. I don't know if I'll keep my subscription though, I'd only be paying for the ESPN networks which is an additional $5 over the base $20 and really the only other thing I care about watching live other than sports is news broadcasts and Sling has a surprisingly limited selection of those.
I'm leaning towards cancelling it after my 30 days trial and then maybe subscribing again next time college football season rolls around.
I understand the HBO add-on has shows on-demand, but I have not tried that trial to see. Yes whatever that button formerly known as the start button brings up some useful options. I was pressing B like you would in Netflix, Media Center, etc.