Does it slow down or drain battery in practice?
I'm using Ka-Block now, after a long time with Ad Block. I'm really liking Ka-Block especially because its description says it "does not have permission to read or transmit content from any web pages."
I'm currently using Ublock Origin but plan to switch to something from the App Store (because assumedly Apple will completely disable non-app store extension functionality eventually). What I like about UO is that it completely removes ad spaces on pages - rather than just blocking the ad - so you've no evidence of where an ad was at all.
Does Wipr do this?
Yes on Mac it is. On iOS you pay a small price.