I agree fully that OEM alarms aren't that great, but the important thing to remember that an alarm is only as good as its install. The problem with OEM alarms is that they are all installed the same way. The advantage to aftermarket alarms is that they are usually installed in difficult to access locations. After market alarms also usually have many features that OEM alarms don't. But, hey, for $66, you can't really beat it.

Oh, and if you have to ask how difficult it is to install an alarm, you might be better off having someone do it for you. They can get a bit tricky.