The open hand has NO advantages, unless the knife guy is a real dummy OR you are Tarzan and you need your hands to hang on to swinging vine.
When I was in grad school, i had the dubious privilege of working night shift in a slaughter house for two weeks.
There were two Mexicans who butchered the steers, and you'd have to see what a real pro can do with a blade to believe it. I'm talking complete disassembly in less than ten seconds.
If a martial arts school neglects knife training, it is because they are seriously out of touch, though, to get really good, you have to do it for real, and if you do it for real you will lose body parts, and spend a lot of time in hospital or jail.
My short term strategy is to be very polite to Mexicans.