I want to share my experience with Focus Thron 2016 and Impulse Evo RS. I imported it from Germany as there were no ebikes sold in my country at this time. No service shops either.
I bought the bike November 2016 and started using it April 2017.
1. When it was ~500km old I had the following bug: When charging the battery it would sometimes not stop when it has 5 leds on and the charger starts making some high pitch noise every couple of seconds. At some point the battery shuts off (some protection), but when mounted on the bike assistance range shows 0km, while battery meter shows full.
I tried contacting Derby and they referred me to a local "dealer" who did not have any cables, or tools for this kind of motor. He said that he had to pay 300Eur to Derby, so that they could send him the cables and grant him access to the system(I think because the bike was bought from another location). So he was unwilling to pay it, just for one customer. I was then referred to the service shops in the neighborhood countries. So, I got used to not charging my battery to the top (using mains socket timer) and found out that even if I do overcharge it, I could slightly discharge it by using walk assist mode for 20 minutes and slightly applied back brake,and that was making the bike usable again. This was more of a software bug, which I wasn't able to fix by updating the system, due to my location.
At this point I gave up of my warranty, that I cannot use without sending everything abroad and waiting for exchange.
2.When 700km old I started experiencing some clanking noises randomly-this was fixed by disassembling the motor and re-lubricating the pawls, which already had some visible wear on them. Since then, I am looking for replacement ones, as spare parts are not available by the dealers, or the manufacturer. They however seem generic, so if someone knows how to source them it would be great. The motor was opened and closed professionally by another bike shop servicing other ebike brands. I had to pay for this myself. There was no warranty-void sticker.
3.Around 1400km (Sept 2018) the support started cutting off when ridden more than 5km on steep trails. Restart was fixing the problem. Later it started doing in randomly . It felt as if the torque sensor was acting up. Later "Waiting for drive" started appearing together with the cut offs. At some point I was not using the bike because I was not sure if I would be able to ride it up back home. This was magically resolved by the same shop opening the motor and cleaning up the torque sensor. Nothing seemed defective, I suppose it was some calibration issue, or another software bug. Torque sensor did have part number, but we couldn't find anything by searching it in internet. The problem disappeared since then.
4.This year ~2000km- after some happy time riding the bike without issues, I rode in heavy rain for couple of hours (it just caught me in the mountain and I had to go back home) - I parked the bike wet in my garage and removed the battery ( as always) to store it in a warm place. Yesterday ( 2 weeks later) I put the battery back on the bike - and surprise surprise- nothing happens- the battery is fully charged, awaken, and still shows 100% capacity, but the display doesn't turn on- as far as I just read here- water damage. I however don't see any moisture anywhere and keeping it 2 weeks without battery should have been enough time for any moisture to dry up, but I don't have other explanation. I will have to check all wires and probably open the display to check for moisture.
To summarize - I have another ebike with yamaha pw motor that has been waaay more reliable, so far (knock on wood), however I really like the Impulse's huge battery, range and higher bb clеarence. I also upgraded the fork and the brakes in the past, so I really like the bike when it works. Unfortunately I might have to sell it for parts soon, as I don't have any more time to waste with this buggy "German quality" motor. I prefer riding, than fixing my bikes when I have spare time.