The coote is a great machine. I love mine
It does have a platen, its just above the wheel. The machine is set up so that you can use the wheel, platen, or slack belt without changing a thing.
I don't know what you mean about it coming with a clamp

There is an adjustable work table, that mounts in front of the platen.
Extra options you can order include, a work rest for the contact wheel, a sanding disc that bolts to the side of the contact wheel, and I think there's some sort of small wheel attachment you can buy also. Its all listed at
www.cootebeltgrinder.com look on the accessories section.
For about $50 you can get 3 speed step pulleys for it, if you can't afford a VS motor. I've got them on my coote, and it works out great. I welded up a big hinge/frame to mount the motor on so that all I have to do is lift it up to take the tension off the belt and switch it to a different speed.
If you plan on doing any hollow grinding I'd suggest you get the 10" wheel. I've run mine a good bit now and like the grind it gives alot better than an 8" wheel. You can stil do small knives on it just fine.