I still haven't received the straps. The idea is to start using them depending on what I've done before and I'm going to do the following day.
As I said, I've bought them to give my forearms a break, so I'm definitely going to use them if I plan to climb the next day or even two days later. Otherwise probably not.
But it also depends on what you want out of your farmer's. For proper full body training I'd use straps. I usually do two kinds of walk depending on aim, psyche, etc.
One session is more aimed at burning fat and increasing metabolism. I do 5 reps of 1' walk with 1' rests in between. I use 68 kg and it's very very hard. Forearms give up and it's quite painful on the fingers. The bar presses them very hard at mid joint.
One other session is aimed at strength, and I do sets of 30" with 108 kg, good rests until failure.
Given that I often overuse my forearms, I think I'll use the straps from now on, except for snatches and cleans, maybe.