Many years back on ADSL it was a case of matching modem to DSLAM just to ensure maximum compatibility. As developments moved on it was no longer necessary.
When BT first started VDSL installs the modems matched te cabinet - just to minimise initial teething issue. Now, you can get either modem with a cabinet.
My cabinet is Huawei and I replaced my Huawei with an ECI a few months back and gained 4Mbps - changing back drops the speed, reinstalling ECI brings it back. I have heard of cases where it can worsen it and also where a Huawei is on a line from an ECI cabinet the results are slightly better. It is a case of try it and see.
M H C
taurus excreta cerebrum vincit