Game consoles lock up, hell, even PCs lock up. A random one here and there, probably isn't much to worry about. Matter of fact, every console I've had locked up on something occasionally.
If it's something consistant, you probably have a problem that is going to get worse.
My views on the system coolers are fairly unpopular, but here it goes. Consoles, more so with the more powerful ones, get hot. The system is designed to compensate for this with various airflow and cooling solutions. If it's getting hot enough to crash, the there is a problem with either your console hardware in particular, or where you have it placed.
If it's a a matter of air circulation because of placement, then the air cooler is possibly a good solution for you.
On the other hand, if you have your console in reasonable airflow conditions (ie: an open shelf in an entertainment center) and it still overheats, the external coolers are just prolonging what you should get taken care of before the warranty expires.
In short, if it's defective, the Nyko fan is a bandaid on what will become a gushing wound again eventually.
Personally, I think these are something that is the new neat thing to have, made popular by the modding community. Somehow some people associate anything running cooler with it running faster. Again, if there isn't another underlying problem, the design of the console should give it proper cooling.