Hi, I think I can help you!
I just recently purchased a Kindle Fire HD and LOVE it. I'm not a huge fan of tablets and never saw myself buying one but I knew I wanted something I could use to make reading easier. I'm not a tablet expert so I can't speak on that but I'm glad I got the Kindle. The Kindle is more of a watered down tablet for the most part. But I can still play .mp4 movies, music, browse online, use all my Amazon apps and content, etc.
With the CBR files you and I were in the same boat as well and I wanted something I could read those files as well. There happens to be a great app called ComiCat
that reads all .cbr files and so I'm able to read all my comics with it. I used to convert my .cbr files to PDF using Calibre but was sick of doing it so I searched to see if there were any apps that could support CBR files as themselves and ComiCat was the one that stood out to me. It works like a charm and allows for a little extra organization with folders and such if you've got a lot of comics. I believe it's $2.99 but it gets the job done. The quality is great with Fire HD screen as well and you can rotate it horizontally to quickly zoom in and read it closer.
Hope that helps! I've been telling my friends lately that my Kindle was probably one of the best investments (that wasn't required) that I've made recently.