The problem with the send to Kindle option is email attachment size limit. For books it's fine but manga and comics are usually too big.
My Kindle is old enough that I was able to jailbreak it and install KOReader so I can just download from my Calibre server directly via OPDS. Otherwise if it's too big for email you'll have to do it over USB I think.
I wish Apple would open source Safari, or at least make some "Safarium" others can build on. Would be an instant third player without all the growing pains.