I disagree the manual switch puts more strain on the rest of the system. What it does is get the engine started. Yes the engine will smoke and throw a fit because some of the cylinders are not firing, but at least that can be a project you can work on later when you get time. If you need your truck to run, the factory controller can and will leave you sitting on a cold morning. It's not a matter of if it will leave you sitting, its a matter of when it will happen. Of course if you plug your truck in every night, you don't even need the glowplug system.
With all due respect, you can disagree all you want but the fact is, in an electrical system and particularly the electrical system on these trucks, if the controller isnt priming as long as it should, that means there is a resistance buildup somewhere in the circuit that should remedied. Having bad or corroded or dirty connections is very common and installing a manual switch to overcome those bad connections increases the heat generated at those points which is really really bad in an electrical circuit. The extra heat caused by longer priming is going to damage connections eventually.
I didnt say that a manual switch itself will put more stress on the system, I am not implying that, I have rigged them up plenty of times, they work fine, but the rest of the system needs to be maintained as well. Installing a manual switch to overcome a circuit in poor condition is not good, it will lead to more severe failure. Like I said in my post, if the controller just outright fails, then a manual switch is fine, but if the controller is functioning but it just isnt priming as long as is needed, that usually means there are other issues that should be sorted out.
With regards to the controller leaving you stranded...The same can be said about a manual switch, theyre just cheaper and easier to replace. They are cheap devices and can also fail, at least the controller has some quality and consistency in them, whereas anyone can go grab a 5$ manual switch off amazon that could fry itself after a week. People have run the factory controller for decades and hundreds of thousands of miles without issues.