Here are our early observations on switching from Fios to Optimum/Altice One.

First Optimum bill, with free installation, will be much higher than you expect because of partial month billing, yada, yada, yada have you signed up for paperless billing?
With triple play, we noticed in our browser window Optimum pop up ads. Coincidence? Maybe.
Our first impression is that the TV picture is much improved with Optimum. It seems clearer. For some reason (VOIP?), when we change channels up or down, there's a three-second black screen that takes over, just enough time to be noticed and be annoying. You can't hold the Channel-up or Channel-down button to scroll quickly... because of that black screen.
We do like the multi-room DVR and recording takes more than one step to actually record (press red button to record, then on show, press record button again.) If you’re watching a show and you press record, it only records from that time forward, not what you’ve already watched [Point to Fios.]
We had some issues with DVR playback. Pictures freeze. Drop-outs. Closed-caption (though available on live recording) not available on playback. [Called chat and a boost fixed it. Until next time when we decided it’s not worth the bother to chat to fix it. Optimum Chat is semi-useless and very difficult to get through. Equal to FiOS chat.]
The Optimum remote is much, much smaller than the Fios remote. Not only is it smaller but it’s much easier to hit the wrong buttons with big, clumsy, arthritic hands, and then try to figure out what happened. Punch in a three digit channel and do it too slow, you get a surprise channel. Someone suggested we keep a stylus handy to change the channels.
The new remote lights up. That’s a big plus when the room is lit only by the TV.
If you like Netflix, there’s a big white button in the center you can use. I don’t have Netflix, so this button is a mistake each time we hit it. The online tutorials were less than helpful. The manual with our password was less helpful.
The onscreen channel display is too small. You can see a number but there’s no way ANYONE can read which network is on because the type is so tiny.