It must be said that some things are very difficult to focus with a rangefinder, furry animals being an example where a micro prism or ground glass is easier. Of course the solution is to focus on the eyes, but if it keeps moving its head you can get very frustrated. I guess if animals are important to you, you will be going down the AF digital route anyway.
If there are lots of vertical lines in the scene it can be difficult to recognise which ones to align, and that will slow you down. I find the best way round this is to focus those subjects with the camera held at 45 degrees, and eventually this has become an automatic action.
The best tip I picked up for speedy focussing (from the late Al Kaplan on another forum) is to habitually return your lens to infinity after each shot. Then you only ever need to focus in one direction, and you press the button as soon as the images come into alignment. I find this makes the rangefinder relatively quick. Most subjects are within the first few degrees of turn of the focus ring. By contrast, focusing with micro-prism or ground glass always seems to involve some to-and-fro.
Naturally you want to be able to use nice lenses at their full aperture. The precision of a rangefinder in that context is part of its attraction, isn’t it? I disagree with those who say it is difficult to focus in dimly lit interiors. If there’s enough light to get a photo, you will be able to focus.
Focus tabs are nice unless you often take photos in portrait format, when I find them confusing - the tab never seems to be where I expect it. You can buy after-market rubber tab rings to fit lenses. I have tried those and discarded them for the reason stated. I’m not consistent over which way up I hold the camera for portrait shots, anyway.