I've had my Kobo Clara HD for almost 8 years and I still use it daily with KOReader.
It's so easy to install KOReader and it's really repairable. I replaced the SD card at one point, and another time I thought it was broken or needed a new battery but came back to life after reseating cables.
Before that I had a kindle and you had to jump through a lot of hoops to install KOreader, and I remember you had to be careful not to upgrade the firmware so it could be jailbroken.
Like I said I've had the Kobo for 8 years, so I hope this is still the case.
KOReader works just as easily, and just as well, on my much newer Kobo Clara BW. I'm not unhappy with the built-in reader software, but keep KOReader installed just in case I want or need it.
Calibre web support, opds catalogue, wallabag, ssh. And it supports so many file formats.
I'd imagine the built in reader has improved a lot over the years, but at the time reading technical pdfs on it was not feasible. KOReader allowed me to rotate to landscape and reflow the pdf text.
I almost got the Clara BW for Christmas, I thought my Clara HD was dead, wasn't sure if it was the battery or screen but it was failing to properly clear and update the screen. Someone actually bought the BW for me but I ended up returning it after I managed to recover the Clara HD.
I was kind of looking forward to the waterproofing, but seems my old one is not yet ready to give up.
I've had my Kobo Clara HD for almost 8 years and I still use it daily with KOReader. It's so easy to install KOReader and it's really repairable. I replaced the SD card at one point, and another time I thought it was broken or needed a new battery but came back to life after reseating cables.
Before that I had a kindle and you had to jump through a lot of hoops to install KOreader, and I remember you had to be careful not to upgrade the firmware so it could be jailbroken.
Like I said I've had the Kobo for 8 years, so I hope this is still the case.