Not on Kindle, but on my iPad I’ve been much happier with the Comixolgoy offerings than other sources… Enough so that I’ll favor them if there’s a choice, even though they lost a lot of goodwill during the Amazon aquisition.
At least on iPad the Comixology app supports a ‘guided view’ mode in which the pages are sliced so you view it at a panel at a time. It sometimes gets clever, like having a page show a big art splash, then cycle through close-ups of text, then show the splash again so you can take it in. It’s a bit reminiscent of the “motion comics” that were popular for a while and makes them much more readable to me.
I have a few from other sources that are .CBR files, PDFs or similar. This includes the Berkely Breathed files mentioned by @RRabbit42 from an earlier Humble Bundle deal (I think I got the Bloom County original run volumes plus Outland and Opus, but not the Academia Waltz or new stuff). They’re readable, but whenever the layout deviates from the standard weekday format I feel like I have to start scrolling a bit (on my iPad Mini, which is a small screen).
I’ve got a few other books in .CBR format: Some old D&D comics from another collection. The app I use on iOS is “Crunchy” and it’s got some good features (a good ‘file manager’ so I can pull files to read from my NAS) but, as I said, the experience just isn’t there.
Do comics bought directly through Amazon use the Comixology viewer and such?