every connector is a sealed automotive connector, all contacts are tin or gold plated depending on the voltage and type of signal that is being transmitted
the control is all solid state and sealed 100% in epoxy....absolutely nothing is going to corrode the control.
I guess time will only tell.
If it will last and holds up to the elements being outside all the time, being washed all the time, in contact with fertilizers and chemicals all the time, hit with branches on occasion and hit by like a back back blower base that will be good if it lasts.
That all in one controller looks expensive if only one of push switches fails and needs replacing.
Also I was noticing the frame that holds the hopper looks very weak, appears from the pictures there are only two pieces of tube frame holding up the hopper and are no supports on them to make stronger.
Many times I've put more than a 150 lb the hopper by putting two or three or bags on top of the hopper to transport them to from the service vehicle.
There are a few other things that I saw that stuck out right away from picts that will be an issue but I will not mention them, I guess you'll just find out in time.
There are some things that look good so please don't think I am only picking away at the possible problems.
It's definitely better than the hydro spreader sprayer machine I built 25 years ago out of new hydro rider. It had individual electric solenoids for each spray tip, each controlled by a switches.