Assuming you aren't asking about the moral implications, the important factors are harm to the machine, or quality of the cheaper product. I've heard of no stories of the harm thing, but was told by an office max person that the refill ink would void the warranty. Assuming they really can tell you used the product, if you are still under warranty that would be a consideration. Beyond that it comes down to quality. I've not heard any bad stories about that, but you should make sure the quality lives up to your particular needs.
Obviously my answer is based on hearsay, I print little enough that the new cartridges aren't a burden.
I have a lot of luck using Google to check a product for pitfalls; use keywords of the product name plus "problems", "rip-off", "warranty", basically what you are hoping to not find.