At Toyota.com's "Build Your Toyota" Configurator, the description of the All-Weather Floor Mats includes this: "...they're held firmly in place with a ribbed backing and a driver's side quarter-turn fastener." (I'm thinking: when the slushy winter comes, I'll probably be glad I had ordered the All-Weather instead of the regular Carpet Floor Mats.) But the description of the All-Weather Floor Mats at the PriusChat Shop does not include those words, leading me to believe the Shop's mats don't have the identical driver's side fastener, which would explain the Shop's cheaper $95 price (half of what Toyota charges) . Am I right? (How important having this fastener is, I don't know.)
Fastener is nice in that it does not allow the mat to slip forward. I believe that in some of the sudden acceleration cases a few years back, it was determined that the accelerator was stuck because of floor mat. I can see why a manufacturer would put them in. FWIW, I have weathertech full rigid floor liners for my Honda pilot and they accept Hondas floor tabs, preventing slip. Common sense and occasional adjustment and you should fair fine without it.