I believe some users deconstructed the Aquariumplants.com electronic CO2 regulator setup previously, and it was found to just contain a solenoid that turned on/off to control the CO2 flow.
If you are unwilling to build your own setup, you can consider the GLA setup. There are also many users on this forum that sell setups, so be sure to shop around.
I would not worry too much about "older" regulator models, since they all work with the same principle in mind. I have used regulators that were (most likely) built in the 70s or 80s and they still worked fine.
below is the reply to a member in my local forum
Originally Posted by Leon Garden
This electronic control does not depend on pressure on both sides of the valve and should eliminate the worry that when the CO2 tank goes empty it will dump the last gas onto the tank quickly. It's sort of expensive -- but so are my fish.
it is the clippard mouse solenoid inside, click once to let out the bubble(flow), 4 bubbles means click 4 times, and 1 bubble per 10 seconds means click once every 10 second.
every time it clicks, the on/off respond time is the same, and with the fixed orifice, the actual flow volume of each click varies depends on the pressure differential.
higher pressure differential(higher regulator output pressure), flow volume of each click is higher, but since the co2 flow "rush" with each click at the set interval, you can't tell the actual co2 injection is actually more, what you see is that instantaneous "rush" which interpreted as a standard volume unit over time.
If I put it this way, may be easier to understand, The electronic system is pretty much like this: under normal pressure differential(set regulator output pressure) is 1 bubble per second, and higher pressure differential(regulator higher output pressure when co2 tank pressure dropping) still be 1 bubble per second, but the second bubble is larger, bubble.