Everytime I look at this topic to see if there is any updated method for drm removal on kindle I see a method going away... I'm so glad I decided to just switch to buying everything on kobo, easy to remove drm and the quality of images on manga is better (not really sure why)... same price (even better in italy I switched from a 3% discount on amazon gift card generated by intesa san paolo to a 4% discount on satispay kobo gift card).
To read on PC I use Cover app instead of kobo app (the kobo app for pc really sucks to read manga as it does not go really fullscreen), to read on a tablet/smartphone I could go with the official app right now but I still also convert to kindle to be also able to use the kindle app (as a reader for manga is still the best on mobile device) but I don't use my smartphone a lot. Right now my kindle 4 is really too small for manga and I think my next manga reader will be basically an android e-ink tablet, I think it would be better to get a device where I can get both kindle and kobo app instead of just one.
Also, I tried to remove the drm from a google play ebook and it works there too so there is another option where I can remove drm and where I can buy manga in Italian.
I was so used to amazon I was a little scared to make the switch to be honest....
The only bad thing is that some books are only available on amazon, fortunately not my beloved manga, but I've already found some examples. I think that in the future the real struggle will be to contact the authors to convince them to publish elsewhere.
Amazon is now a lost cause, their drm is likely to be broken in the future but it is also true that they are doing everything to keep it updated which means that any holes are unlikely to last long.
Obviously both books and manga are nothing more than a set of writings/images so in desperate situations you can always proceed manually with the creation of a DRM-free version by copying by hand/taking screenshots. But as long as you can avoid it, it's definitely better to avoid it.
I still advice those who can to switch to Kobo or other good alternatives at least for ebook where it is possible, even if you got a kindle device just use kindle previewer 3 to turn the epub that you got from kobo (drm-free or where you removed the drm) into a compatible mobi/other format compatible with kindle... or just use
https://www.amazon.com/sendtokindle (the quality for manga/comics/images epub will be worst than using kindle previewer and you will need to divide epub with more than 200mb in pieces but on the plus side you will get the epub on the cloud).
Do not support amazon if you can avoid it.