> An argument can be made the rental is worth it for the ability to tell them "if I can't get x speed off this Ethernet port, it's your fault, hands down, so fix it". Whether or not it's worth $10-15 a month depends on how much you loathe arguing with Comcast on the phone.
You can still make that argument by plugging a computer directly into the modem. It's not a good idea for long term use as there is no NAT so your computer will directly receive all traffic for your public IP but it's fine for the initial setup when you're verifying that your supposed “up to X MB/s" is really "barely Y MB/s".
This discussion here is really on renting or owning your own modem. As far as I can tell, most rented modems now bundle a router/access point into the modem confusing the issue slightly, but you can (and should IMO) buy your own modem. I have refused to use any ISP supplied hardware for well over a decade precisely because of issues like the one described in the article.
You can still make that argument by plugging a computer directly into the modem. It's not a good idea for long term use as there is no NAT so your computer will directly receive all traffic for your public IP but it's fine for the initial setup when you're verifying that your supposed “up to X MB/s" is really "barely Y MB/s".