3.1 is "future proof" since 4.0 is still about 2 years away (mid 2021 last I read), but 3.0 will still be around for quite a while.
I always find it funny how others like to tell people how much bandwidth they will need. Everyone has different needs, and your needs are not my needs.
I personally am just fine with my 65 Mbps speed (I think Comcast just upped it to 75?), and the 100Mbps my mom has is way overkill for her needs (but is best/cheapest value combo with cable).
My DOCSIS 3.0 Surfboard SB6141 modem is just fine for me, and has been solid since I started using it in 2014. I had to upgrade to it when Comcast dropped DOCSIS 2.0.
I got my mom a Motorola MB7220, and while a 8x4 DOCSIS 3.0, it allows 110 Mbps on her 100 Mbps plan.
The Surfboard SB6183 is 1/2 the price of what you linked to, but will give you 175 Mbps (and would be fine up to ~350 Mbps) even being DOCSIS 3.0.
DOCSIS will be around for at least 2 more years, probably closer to 5 till it is dropped completely.
I know around me, DOCSIS 2.0 was around till 2014, and DOCSIS 2.0 came out in 2006. One of the big reasons DOCSIS 2.0 needed to go was it did not support IVP 6, and IVP 4 was running out of addresses.
So Spectrum gives you a modem and Comcast doesn't. Probably in the base fee. Go figure.
Comcast charges $5-15/month for a modem (cost varies on location).