Referencing "models" is weird to me to start. Now I'm thinking of a designer who has a bunch of "hot chicks" directories on his computer. The intention should be that "high quality photography" will make most designs look a lot better, not the "high quality" of the looks of the human subject, right? When you make it about "models", you've made it content-specific, and this is compounded by making it gender-specific with "hot/nice girls". How about:

Any design mock-ups look fantastic with high quality stock art, but can it pass the Trial by Co-Founder™? Replace your professionally photographed imagery with a random photo of your co-founder and see if the design still "works".

You could also go for something like "sexy boys and hot girls". Models on it's own works perfectly fine though.