Unfortunately Roku no longer offers the Spectrum TV app. Just did some research on the Spectrum website.
You can just screen mirror it from off your phone or tablet. I do that when I watch random stuff that isn't attached to an app.
I have a 58" Onn Roku TV (was a $200 Black Friday deal) and it works pretty well. About as smooth as when I used a stick. Only issue I have is if the remote messes up there is only a power button on the TV. There is a Roku app that let's you use your phone as a remote so it's a good backup.
You can also plug earbuds in your phone (wired not bluetooth or there will be bad audio lag) and listen privately with the app. Now the Vizio that we put in my daughter's room ran like crap with their apps. I only used sticks on it. Maybe higher end versions of that brand work better.
Speaking of sticks, the Amazon ones suck compared to the Roku ones I have had. It's like they don't have enough RAM and they lag and freeze a lot when searching through it. Probably doesn't help with all the Amazon garbage that is attached to it. If you aren't heavily invested in Alexa products I would suggest to stay away.