Here is the real reason not to use DOT 5. That crap is VERY VERY difficult to bleed. It can be an unbleedable world class horror sometimes. The air moves so slowly thorough the silicone that you almost always have to use something like a MittyVac or such to get the system bled.
For a few years there, Harley used DOT 5, my 03 being one of them. They used it because it was less harmful to paint. Visit a Harley tech site, and do a search for brake bleeding DOT 5. Read the horror stories and screaming rants.
Don't listen to the guy. Silicone has to be flushed and changed just as often as 3 & 4, and it is HELL to bleed properly.
But what do I know? I'm old.