I would recommend the GinSan version over the IDX MX-8. It's nice to have the delay, but it's not really that big a deal. I've worked on a wash that had seven or eight IDX units, and after five years half of them had gone bad where the output would randomly not work. The GinSan GS-16D is a little easier to work with since you just get power from each solenoid or pair of solenoids and run a pair of wires to each of its inputs. When you combine all the "common" sides of your bays to use the IDX, you have to ensure that all the power is in phase or you may have issues elsewhere.
In the photo you quoted I used relays there because I was trying to find an electrical issue and I wanted to completely isolate the bays from one another electrically. The relays were a quick and cheap way to do that, and if I were building or remodeling a wash I'd use relays again. In fact I pulled a bunch of PLCs, relays, and a failing control system out of a wash and replaced it all with relays which saved probably $300 over multiplexers.
Another I did a few months later, had three boxes full of relays like this plus twice as many PLCs
