I use a Kindle and pretty much exclusively sideload. The display and form factor are fantastic. Battery life is very good. Last time I was in the market (late 2021), nothing else was as good.
Except when you can't, like literally yesterday: subscribed to Asimov's, sent ePub, got a link, clicked a link, "that link is not valid". Repeat, same message. Why? Who knows?
My next ereader won't be a Kindle.