Well it's really up to you mate.
It's just personal preferance.
some people find them constricting making them not as mobile and comfy on a field.
other people worship them because of those evil neck shots you can receive from a good 'ol bunkering.
i can depend on what and where you play on a field.
as a back-man i don't wear one because of a variety of reasons.
1) i get very hot and steamed up.
2) i cant communicate as well
3) i don't tend to get bunkered alot at the back.
i think if you were playing nearer the front of the field looking into a neckguard is a good idea.
but as i said it's all personal preferance.
Pick up a cheap rhino one or something and try it for a couple of games.
there's no harm in trying.
hope you find your awnser.
balloon