That particular program is best suited for work between friendly parties who want their correspondence to remain private and want it to self-destruct after set periods of time. However, both QVtech's Interosa and Authentica's MailVault products are more adept at stopping rogue recipients. Interosa, for example, forces recipients to display all of their messages in a special window that limits the ability to manipulate or print the contents. Of course, the receiver could make like a spy and photograph the screen. But perhaps you shouldn't be sending an e-mail to someone with those inclinations.
Common sense is the best guide.
The advantage of these new systems is that if the expiration date is set for, say, five or 10 days, then the messages will be unreadable long before they could be discovered and used in litigation. That's where the real value lies. However, these purges should occur in the normal course of business. Otherwise, it could appear that a company is destroying evidence. Authentica is the only developer actually shipping a product.