There are plenty of other controllers available that would work. But the rk2001 seems to be an industry standard as several different mfrs use it. But if you want USA made it is available through ahona.
I'm typing this next part slowly so you understand what I am saying.
I could buy the same aquastats, relays, timers, temp gauges etc. and bolt hang or tie them to my boiler. But i dont think the cost/benifit of using standard off the shelf parts is worth it. AHS seems to have come to the same conclusion as they are now using printed circuit boards. I imagine it costs several times as much to replace the functionality of circuit board with standard relays timers and aquastats.
If and when I run into a situation where the controller is broken and a replacement is unavailable I could use the same control strategy you are using with off the shelf parts. You just paid for the standardization up front while I'm taking a calculated risk that if the rk2001 ever breaks then a replacement will be available.
Hope that makes cents.
By fine tuning I meant things like the right settings on the cycle timer to not lose a fire and how to stop the back puffing.