From a guy that has actually put over 100 cord through a splitter with auto-cycle.
Prince still offers them, they are on the website, and as far as I know they are available through Surplus Center. I installed one several months ago on a TW-P1 for a friend and that's where I ordered it.
Having one on my Timberwolf TW2-HD is the best thing ever for increasing production through the splitter.
I think a lot of issues people have with these valves is the do not always function as they're intended until the hydraulic oil is up to temp. So in the first few splits they start screwing with the adjustments and getting the whole system out of balance. The Timberwolf dealer I purchased mine from used to see that all the time and getting it back in tune after the the user had screwed with it was not covered or paid for under warranty. When adjusting the settings on the auto-cycle 1/8 of a turn is usually all that's required.
In terms of safety, all the crap and horse manure about them being dangerous is complete and total BS nonsense spread by idiots and jerks that have never even used a splitter with auto-cycle. Think about it, if you're operating the valve / splitter the way it is intended, you will be no where near the splitter, as you will be staging the next piece during the cycle. My splitter has a 13 to 15 second cycle time and it's usually waiting for me and the next piece. In short if I'm 4 to 20 feet away from the splitter during its up and back strokes, that is a whole lot safer than standing next to it waiting for my hand to get caught or a split to fly.
Take Care