Ready loads in Polaroid 545 holder?

I was thinking about shooting some ready load/quick load film with a 545 holder, but I was told that the 545 doesn't hold film flat enough. Is this true? Anybody use a 545 holder for ready loads or quick loads?

readyload use

I've shot probably a dozen shots of Ektachrome100VS through a polaroid 545 holder, though not the metal one. Although I think I did shot a couple through an old metal 545 holder. I used to carry around a Kodak Readyload holder AND a polaroid 545. I've since sold the Readyload holder, if that helps you at all. I've had no problems with film flatness, but ymmv.

Here's a shot done (I'm almost positive, but I drink a lot) with TMax100 in readyload in a 545.

Here's another one where you can see sharpness throughout the image...