I bought 2 of them, and have been using them the last few days while I build a new hay feeder for my animals.
They seem to work pretty good, and believe it or not, the side guides are actually square!
I will say that dragging steel across the tops, scratches the 'anodized coating' fairly easy...
Get a cheap fish scale (or 2) to use to get a good 'pull' weight at the point you want to attach your cylinders. This should tell you almost exactly what rating you want them at.