My friends with flow love them. I got rid of the straps about 9 years ago when Burton made their first step in and have not looked back. the new SI/RulerSI setup is so amazing that its hard to believe that people still use straps. I lock into my boots and I am off and running. I click in whlile sliding down the ramp at the ski area and I am off. I have been riding for about 14 years now and i am an advanced rider (i ride a 169 Nitro Shogun). They are very stiff boots and your foot is very securely put in place.

The old notion of your boot disengaging has never really happened to me. no wiggle side to side like the very old first generation did. Snopack is a light concern, but it is with any boot/binding setup. you need to scrape your boot before putting it in the binding if it is

The downside with SI is the need to pick a vendor for boot and binding. For me it was not an issue, since I love Burton Soft goods (boots, gloves). IF that is a big concern for you, then flow would be the second choice.