I have the spyder express which does an adequate job.
The dearer calibrators do a better job and give you more functionality.
Its down to what you can afford.
The first thing you will notice is that monitors are cold by default, eg very blue. the calibrator will warm up your screen and at first will most likely look very pink.
Often a 10 second look away then back again and it looks great. A lot is down to what you get used to seeing rather than what is actually correct.
Some of the dearer calibrators calibrate not only your monitor but your printer/scanner to.
this is often overlooked and is just as important.
at the end of the day, its like a work flow, you set your camera to take pictures in the right format eg, SRGB or ADOBE RGB then you need to calibrate your monitor so that you see the same as your camera see's.
Then you need to calibrate your printer so that what you see on the monitor is what you get on print.
Im no expert but it can become quite a headache if you get this wrong.
Once setup correctly though, it'll save you a fortune on printing off five prints each time to get one correct one.