Just signed up for Comcast's Instant TV a week ago. For $69.99, every channel I get over instant TV is exactly what I already have from a digital antenna. No cable channels whatsoever. Basically, a pointless service. BUT! They've bundled it with a 150Mb down/20Mb up internet package. For $69.99 I'm now getting internet speeds that test at 175/24. ...oh yeah, and this Instant TV rubbish. (and my contract was coming up, so it gets me re-bundled for the year's discount)
See, I've also got Sling. So, I can compare. First thing: Xfinity's app for Roku is a bugged up nightmare that only half works, so watching "Instant TV" on your TV is not REEEEALLY an option right now. On your PC, in browser... seems to work alright. Next thing: Pretty sure Comcast's Instant TV is all in 720p. Yeah. 720p max resolution in 2018 from basically THE cable provider in the U.S. So, if you've got a nice 52"...well, enjoy the low-res digital blur from cheapskate Comcast. Next thing! ... Wait, no that's it. There's honestly not much to say about it. Or... reason to watch it.
They've rolled out this internet-tv product with a channel lineup designed for your grandma - all local, no cable - except your grandma wants a set top box and proper, old-school cable! The market they're appealing to wants to lead the edge, cutting the cord with Netflix, and YouTube... and Comcast's product offering maxes out at a 15 year old resolution. (Helluva marketing team over there.) At the price they're selling it, and with the lack of channel offerings, it's not really a product. There's no reason anyone should (or will) buy this outright.
But if it keeps you in a discount-package, (so you're not being robbed by their "regular rates") and you can get Comcast to sell you it's 2nd highest-speed internet package with it in a bundle... well then! You're still going to need Netflix and Sling.