my attmepts at yer questions are not in order, but here's my thoughts:
we've used those to backfill tank excavations and the compaction is good enough to stabilize fill near building foundations and where traffic will be. i've only seen it used on road base materials not clay. also, i've only seen it used on flat, i dont know how it would be on slopes. on clay to seal water, i dont know if they'd achieve a better compaction than a big sheepsfoot....somebody here should know that.
the surface area and psi of a big sheepsfoot i would think is much higher. there could be a bang for the buck issue there with the drum roller, it might be better than nothing, but not as good as having yer contractor use a sheepsfoot. the moisture of the clay will be very important too.....not too wet, and not to dry, but moist.....that's how you want the clay for best compaction.
at the same time i know of successful jobs filling in small lifts (<1 foot) and just using the dozer, the key is small lifts.
the vibro drum roller is cool, very fast, but you'd have yer hands full to cover 5 acres in two days....if you get it make sure it has lights and be prepared to stay up late.
