The pedestal feet are designed to be placed directly onto the concrete. I believe once you've built this platform, it should be rather solid and heavy, and I can't see it really moving anywhere. I have heard of the feet being glued down to the concrete with construction adhesive if you are concerned about movement.
There is another style of foot designed more so for pavers. It doesn't include the handy tab to screw into the side of your joist, though. However, it has holes in the base to be bolted down to the concrete. You could use these by screwing the top plate to the underside of the joist. You'd then attach their base, adjust it to the correct height and then bolt it down to the slab.