For the past few years i've been using OpenWrt to successfully combat bufferbloat on my VDSL2 connection (see my blog post for my setup, including UK-specific tweaks. Although i'm now using SQM-scripts instead of QOS-scripts).
In all that time i've been using the ECI modem that was supplied to me when i first got VDSL2. With the advent of G.INP being introduced (and because my Zen line stats seem to have been broken since February) i decided to try out the Huawei HG612 i've had in a box for the past couple of years. I updated it to the latest hacked firmware and after swapping it in for the ECI i experienced some weirdness.
After swapping it in i did a simple bufferbloat test of running a continuous ping to bbc.co.uk while running a speedtest. During the upload portion of the speedtest my pings jumped from 18ms to around 100ms. I was only able to get them back to around 21ms by dropping my upload speed to 5000kbps (was 5500kbps using the ECI modem. The Huawei sync stats showed 5626 for the upload while my last Zen upload sync stats showed 6628 using the ECI) in SQM-scripts.
I then decided to run the recommended netperf-wrapper tests.
Here's my RRUL graph for the Huawei HG612. I'm not too clued up on how to read these but i think ideally you want the average line to be as smooth as possible. With the Huawei the download speeds are all over the place and i suspect i'd have to limit the download speed in SQM-scripts even more to improve things (it was set at 90% of the sync speed as reported by the Huawei).
Keeping the exact same values in SQM scripts i swapped the ECI modem back in and reran the test. Here's the RRUL graph. Much smoother, with almost half the latency.
So i'm sticking with the ECI modem even if it lacks access to the line stats and G.INP (which i don't think my cabinet has yet anyway). I was also able to bump my upload speed limit back to 5500kbps with no effect on latency.
Line Stat details:
As reported by Zen (last updated 26th February): Upstream=6628, Downstream=33878, Sync Rate=35000
As reported by Huawei: Upstream=5626, Downstream=34998
Speed limits set in SQM-scripts: Download Speed=31500kbps, Upload Speed=5000kbps