There's no denying the Perkeo II is a nice size, I own one that I use a fair amount. I have found I do well enough with estimate and set to leave an accessory rangefinder at home. I've probably messed up focus more often by getting absorbed in the moment and forgetting to do it at all!
I will note that while very compact, its weight is surprising, almost 1.25 pounds/545 grams -- not really heavy, but a sense of substance. Of course it dates back to when things were actually made of metal and glass!