I’ve had a somewhat bad experience with Côte et Ciel, albeit with their Nile bag instead of the Isar.
https://www.coteetciel.com/en-US/nile-backpack-obsidian-laptop-bag
I owned it for about 3 years. After about a year and a half or so in, the shoulder straps started being defective - they would always slip down over the course of a few hours, which made wearing the bag with any kind of load fairly uncomfortable (and probably bad for my back). I emailed their support, and they basically told me it was out of warranty and there’s nothing they could do about it. However, later they added this exact problem to the dropdown list for their online support system, so it’s clearly something they knew about.
Then last month, the zippers started unstitching over ~10cm or so. I again contacted their support, asking if there was any way to fix it - and that I was happy to pay for it. Once again, they told me there was nothing they could do about it. They offered to send me a replacement zipper, which I have still not received.
It’s a shame, I really loved their design, and as a French person I wanted to support a company from my home country - but the fact that they don’t stand by their products (lifetime warranty tends to be the standard for expensive backpacks) really turned me off from them, and I doubt I will buy anything from them again.
I replaced my Nile with a Timbuk2 Bruce, which I really like so far. Kind of a similar aesthetic, more comfortable, and holds more stuff. We’ll see how it holds up, but Timbuk2 has been good in my experience - and they do offer a lifetime warranty.
http://www.timbuk2.com/bruce-pack/1398.html