For my mobile tool set I took a relatively cheap IT tools set once, organized in the large book sized faux leather case by various loops. Then had it gradually improved to my tasks, adding other or better tools, modifying them, making sure some could mate with each other, fit with other tools in the case, and removing less used, redundant, lower quality, or lesser versatility tools. So the answer is - build your own anyway. Just find a way to organize it well.

The LM Wave + bits kit is my EDC, however for a serious field work you will often want something a bit more effective. E.g. my 12 years old Black Decker VersaPak screwdriver is still kicking and comes with more than a 100 hex bits collection (60 of them are special security screw bits), my mighty pliers are 10" long, 3 full size hack saw blades with a handle, and so on - all fits in that relatively small field kit.

The separate automotive kit is always in the car (all metric) - also self assembled over the years.