I've seen things about this, but I'm not convinced there's enough value in going to great lengths to replace that particular piece of equipment.
In the case where the terminating equipment is a small box that exposes ethernet, with no routing or otherwise interfering the function of my own router, I think it's good enough. An argument could be made for the all-in-one devices, like saving some power.
I get the geek factor, and it's one of the reasons why I run my own router, but for this specific bit, which needs to be fairly well integrated with the ISP's network, combined with their usual abysmal support, I think it's a better bet to just leave it alone.
For me the issue would be that they mandate the user traffic to be vlan tagged but their modem only exports 1000BASE-T so it's physically impossible for me to get the full gigabit of Internet they sold me.
They most probably sold you 'up to 1 Gb' bandwidth, not just '1 Gb'. Overhead is about the same in these cases. Your losses are negligible. It's more painful having 4-5 (on worst time periods/peers) or 6-7 (on best) of the 'up to 10 Gb' (clearly sold as such) fiber access I have.
Legally they are physically unable to provide the gigabit they claim I could get.
That's the problem here.
Sure, due to the shared medium nature they do not promise to always have even particularly close to a full gigabit available for me, but that's documented according to the 3 residential internet SLA thresholds the BNetzA (Germany's FCC; except they also regulate power and gas grid) defines and that a provider has to cough up numbers in an info sheet at the time of sale.
The issue is that if they are physically incapable of delivering the up-to they sell and it's not due to the unpredictable nature of e.g. radio reception strength or POTS wiring quality (ADSL), this very quickly very strongly reeks of fraud.
Even just a little bit is fraud, just as systematically under-delivering e.g. gasoline would be. Think if you bought that in cans and they say they're e.g. 5 gallon (or 20 liter) each, and at nominal temperature, none of the cans you can actually find for sale end up having the full quantity, always being at least an ounce (~30ml) short.
In the case where the terminating equipment is a small box that exposes ethernet, with no routing or otherwise interfering the function of my own router, I think it's good enough. An argument could be made for the all-in-one devices, like saving some power.
I get the geek factor, and it's one of the reasons why I run my own router, but for this specific bit, which needs to be fairly well integrated with the ISP's network, combined with their usual abysmal support, I think it's a better bet to just leave it alone.