don't listen to what these guys are saying (except 11.4)...tho doesn't seem that you are anyways, good job

people have ridden straps with shoes just fine that functionally hold, despite slotted cleats being the best/technical/proper option

I've never had toshi's but that's weird that they are slipping. mayb adding twists will also change the latched area on the strap to a less worn portion and allow you to still run those. I have kashimax singles, have left them out in the rain numerous times, and they still hold my foot pretty darn well until I reach down and loosen them....and I mash (and PULL hard) up a long steep hill first thing every morning