I'm officially a very recent flat pedal convert. I've been using clipless for years and before than only used old school touring and ubiquitous cheap slick all-plastic pedals before then.
Trying these new screw-cleat platforms feels like discovering a secret that has long been kept from me. They're every bit as secure as clipless and using these pedals is breaking me of a lot of bad habits instilled in me by clipless. It's really nice being able to wear any footwear I desire and be able to throw my foot out without having to fight to get back in while climbing rough terrain.
Contrary to my preconceived notions, I will not need any clips or straps with these pedals. The grip is that good. I do not see myself going back to clipless even when the weather warms up.