Having had the VR900 for a week+ I've pretty much decided not to keep it.
It's half decent, but I found that on my particular line, which syncs at approx 35Mbps+/7 Mbps, the VR900 would consistently only sync the upstream at 6 Mbps. It doesn't sound like a lot, but I do a lot of uploading/online backup. I've synced a few times ir VR900, to HG612 and back.. and the difference is real, supported by speed tests. Downstream appears very very close, and SNRm for both directions at the speeds I mention is about the same.
My experimentation (albeit more with the dodgy HH5a) has reminded me that keeping a stable VDSL connection is essential to avoid the wrath of the DLM gods, thus making the case for a one box solution less clear. Additionally having used the router a little it's still relatively simple -- no adaptive QOS, VPN server or other fancy config, and just perhaps for me if I was spending the money a more customizable option running ddwrt might be better.
I've contacted TP-Link about the vdsl observation.