I own a Clara HD. I don’t find it sluggish (quite snappy unless it’s trying to render badly formed PDFs, there is no ghosting after 3 years of regular use and my inputs are never wrong, but I have been using Koreader on it for all but month 1. It sounds like your screen is polling too slow if you’re getting misinputs, or something else similar. Not an amazon product and doesn’t give me ads either.

Calibre is baked into koreader but go off. I was asking about sluggishness.

You find Clara sluggish with KOreader?