Just to clarify, making a bootable clone of your HD using SuperDuper is FREE. You are allowed to make as many clones as you want. In no way is this feature crippled, buying a license will not make it run any faster or better.
Shelling out the measly $20 license fee will give you access to additional SuperDuper options, perhaps most relevant being the "Smart Update" feature. This feature allows you to sync your HD with your cloned backup, negating the need to create a new clone everytime you want to backup. Basically cutting a 1 1/2 hour process into a ten minute one (you will of course need to make a clone first).
For full peace of mind, SuperDuper is an invaluable app. I can't recommend it enough. And the developer is very committed, this app is constantly being improved. Give it a go, I'm certain you won't be disappointed.