I've been running Zero One since 1980 and have never seen the point of changing.
It was very advanced in its time, had the smallest loco chips, when compared to the larger Airfix ones, and used the Texas Instruments TMS 1000 micro controller, the first of its kind in the world back then.
The TMS 1000 was a 4 bit RISC type processor with built in I/O ports and was used in everything from expensive washing machines to fuel injection systems. It was cutting edge technology back in 1979, when microprocessors where very expensive.
My son grew up with Zero One and had a hard job understanding a friend's traditionally controlled layout especially the part with controllers being assigned to control a particular piece of track and not a specific locomotive.
For end to end or branch line terminus operations with limited space, Zero One, or any other digital control system is idealy suited. Being able to cram in locomotives onto a parking siding, buffer to buffer, rather than seeing a 0-4-0 shunter with big gaps in front and behind it on an isolated piece of siding intended for something like an 4-6-2 tender locomotive, is more prototypical.
My current small town branch terminus has a foundry spur and works, complete with scratch built travelling working crane, which has a slight incline to reach. Having a foundry gives a good excuse for a lot of interesting and varied rolling stock, locomotives and loads to venture onto the branch line.
Occasionally, as real pieces of metal are used for wagon loads, there is the need and spectacle of having one shunting engine pulling and one or two shunting engines pushing a heavy load up the incline into the foundry exchange loop. Usually all the engines are on a seperate controller or spread between two. No traditional control system would allow this, only ye olde Zero One or modern DCC.
Some of my shunting locomotives are kit or scratch built or convertions and range from an old re-underframed 1960's Jouef North British 0-4-0, Hunslet 0-8-0 to an Airfix "Pug". All are under Zero One control.
Even the Hornby "Jinty" and Tri-ang C-14 "Polly/Nellie/Connie" have been "chipped up" with the device in one of the water tanks. No need for a permanently attached wagon.
The main faults and repairs with the Zero One are as follows:
Original single Triac chips burning out on old Tri-ang power bogies...
Actually this isn't the actual chip burning out but rather the small isolation capacitor, mounted on the board as a little blob, not having the right current rating. To repair just solder in a 100 pF. capacitor across the burnt out blob's tracks and it'll work again. I've one that I repaired over 20 years ago in this way and it is still going strong.
The Zero One keyboard not working....
This is where the silver paint on the underside of the rubber membrane has worn out. Two ways of fixing this, one is to super glue silver foil onto the membrane to replace the worn off silver paint, the other is to install microswitches. The microswitch idea can be expanded by wiring a 9 or 25 pin D-socket intto the side of the Zero One unit and having keypad stations around a layout.
To break into a Zero One casing, after unpluging it from the mains electricy supply, is to use a soldering iron to melt out all the brass rivets holding it together.
Inside it is pretty straight forwards to remove the keyboard and to understand the layout of the matrix contact connections. It was built down to a budget and this makes it simple to fix as most of the faults surround the construction rather than the actual computer electronics. With age some of the wires, particuliary to the speed control slider will become unattached.
I've repaired many Zero One controllers and perhiperals over the years, for my own use or others, and anyone who can wire up a layout or repair model locomotives can repair a Zero One controller, once they have figured out how simply it works,
So never junk a broken Zero One.... it might just be something simple that needs a bit of soldering or glue to fix.