Please do not buy Michael's economy frames. I bought about $400 of them and had to throw all of them away. The foam sides started crumbling and little bits of crapola would get all over the posters when displayed.
I'm also less than happy with some of my Spotlight frames nowadays. The clamps have too much pressure and can quickly permanently warp the poster. However, the pressure is inconsistent, so some frames are fine. Also, Spotlight now gives you thicker plexiglass, so it's less of a problem
So in the end, I'd go with HPF.