The cheap ones tend to butcher the crimp terminal. I've got a set I bought off ebay andwhile they do the job the dies tend to pinch the sides of the terminal so you end up with "wings" where the die halves contact.
A decent pair of ratchet crimpers are definitely a good investment. I have a pair that takes interchangeable crimp dies. They aren't cheap but you know that the crimps are going to be solid.
Ergonomic Supercrimp Tool - Jaycar Electronics
The last set of dies I bought were for the AMP terminals used on much of the Td5 engine harness. It's pretty handy being able to swap dies, rather than having a multitude of crimpers.