They used to look a lot worse but the routing was changed to TBB and the charts improved quite a bit. The charts are not indicative of the whole service, as whilst before the routing change they did look pretty poor, monitoring from f8lure did not show the same thing for me and was quite flat.
For good measure I stuck a spare BQM on the witless gateway I'm on, then I can see the difference. I've always found it interesting there is quite a bit higher static latency through the BTW network than Zen's own, something I observed when with Zen and switching between BTW and GEA. I guess Zen probably go something much more like point-to-point between exchanges and their network than BT do, with more hops that we don't get to see.
When I was on Zen backhaul the charts were flat as a pancake (never seen BQMs so clean), even when using the connection and maxing it out, and I suspect Zen have some direct connection to the testers or prioritise the packets as it was suspiciously too good. It should be noted that when I maxed out on Zen I could never get speeds as high as I do on AAISP, even though the BQMs looked like the ideal connection!
I think looking back on it that there is a lot in that. I did point some BQMs at the Zen gateways and they looked terrible, whereas the AAISP gateways look like my BQM but with a much lower latency floor. Though of course a difference could be that the Zen gateways are doing all the routing in hardware but responding to pings is a CPU task.
Someone did share a BQM from Cuckoo (TTB white label) and that did look very similar to Zen.
Anyway, given the performance is so much better on AAISP for me it's largely academic.