I use Diskeeper Pro 9 and am very happy with it... However, before purchasing, I did trial PerfectDisk and as a result of registering the trial I receive fairly frequent offers to purchase PerfectDisk at a discount (they now go directly into my junk mail folder and are deleted so I don't know what the current offer is...). They also offer anywhere from 20 to 35% discounts for people cross-upgrading from registered versions of their competitors' products (particularly Diskeeper).
If you've registered the trial, someone in sales will likely be in touch with you with an offer to purchase at a discount. If having a fully registered version isn't urgent, I'd wait for a few weeks and see what happens.