Purchased the ADV 8.9e nearly four weeks ago, so thought I'd register to share my thoughts as this is pretty much the only forum I can find discussing the model.
Anyway, initially things are pretty positive. There's essentially no drag from the motor when going above the cutoff, so it's pretty easy to maintain speed. Very handy for commuting and not building up too much of a sweat.
Range varies massively, but I see the motor as there to flatten hills, not do all the work for me. So to that end I keep it to minimal assist and only use the higher modes when the gradient warrants. The other day I managed 53K and 900 metres of climbing and still had 39% left by the time I got home. I weigh 15 stone, so I was pretty happy with that.
I've made a few changes, such as swapping the seat (which is honestly haemorrhoid inducing), inverting the stem for comfort and replacing the tyres with something tougher than the tereno zero pair it came with. I've also converted to tubeless, though after ordering a new set of valves from DT Swiss because only they seem to sell ones specifically for asymmetric wheels that the Boardman is supplied with.
At some point I also plan on changing up the drive train somewhat. I'm going to change down to a 38t chainring and also try a 11-46 cassette which I'm pretty certain will fit. A new 650b wheelset with 47mm tyres is also on the cards which means I'll have a bike that can be geared and specced for flatter and faster as well as steep and rough.
As for downsides:
One of the seatstay mounts for a rack was crossthreaded from the factory so I had to use pliers to get the bolt out after rounding off the hex head.
The lock is a bit finicky sometimes and requires an uncomfortable amount of force to turn on occasion.
The torx bolts on the gearbox weren't tightened correctly so I had creaking from the 'bottom bracket' after a few miles.
There also appears to be a missing cover plate on the back of the gearbox so you can see exposed wires. It's this normal?
The brake levers weren't lined up properly so out of the box they were pointing in completely different directions.
I wish the downtube unit sat more flush.
Fazua specifically, I can't figure out for the life of me why it only connects about one time in ten to my Garmin head unit to display battery and power etc.
Overall I'm happy. Wish the discounted Vitus e-substance was on sale at the time I bought it, mind, as that's more suited to the type of riding I do, but that's just one of those things!