I prefer the Rainbird. All the different brands are easy to use for the homeowner.
The installer sounds like an idiot. I would have him put in his 'overkill' product.
That way if it breaks, he will come out and take care of it.
It sounds like he doesn't know what he is doing and hopes you buy the timer so when it breaks and you call him for help, he will tell you he cannot fix it because you bought the timer. Furthermore, it he does decide to fix it, I am sure he will charge you.
I have seen more morons in the irrigation business than ever before. I think guys get into it because it pays better than mowing, but they are trained and knowledgeable like they should be.