If you look at Optimum’s support page, you’ll get a list of supported modems. Almost none of those are actually available for sale.
On the bottom, they tell you to go to the website http://www.arrismodemsitecsc.com/ to buy a modem. This redirects you to http://shop.surfboard.com/optimum-store/ which now shows nothing, but yesterday showed two out of stock modems and one pre-order modem. These are the officially supported modems.
There are multiple websites that tell you there’s a whole bunch of approved modems, but Optimum officially supports just a few models, mainly from Arris. Others may work, it might not. I specifically looked for a comment or review that said “I bought this modem and it works with Optimum.
Have you considered just buying an inexpensive modem off Amazon and trying it out? If it doesn’t work you can always return it. The one I bought (link above) is $50 shipped.
First, the “rental” cost I am paying is about 60 bucks/year. I certainly have looked at supplying my own modem, but when I took my last look, third party modem/routers that supported 892,11ac were all in the 200 range, so “payback” was under 3 years. BUT I also use their phone service and no third party modem/routers seemed to support it. Yes I WOULD get a “free” box from the cable outfit, but that means I now I have 2 boxes to deal with.
If anything happened to any third party box I get, boom, but another one. If I THINK there is any issue with my hardware, I can take a short hike down to their storefront and swap it for another one.
Trust me, I HATED to come to the conclusion that it was better to go with the cabe outfit’s box. Then again, I sliced their TV service right off my monthly bill, saved about 85 bucks/month. Yes I am in a former crime warner now spec-doom area.
802.11ac is a router specification, so you must have been looking at the price for combined router modem. Modem use DOCSIS specifications and they should pay for themselves in less than two years.
Understand that phone service is a factor here, but not sure why dealing with 2 boxes is a problem. It’s actually an advantage to have single use boxes since technology advance timing is different for them. Replacing individual boxes when they go bad or obsolete will be more cost-effective in the long run. See “Combination Modem-Routers: Not the best of both worlds” in <https://www.tomsguide.com/us/modem-vs-router,review-4246.html> as an example.