First find out what the local players are on and make sure you can talk to them. No point in having an uber radio if you're the only guy on the field who can talk to yourself. No point in a radio shack bubble radio either if there is a decent net already in place.
Second make sure you can run a headset and mike with a PTT switch and factor that cost into the purchase. If it's just loose on your vest and squawking away everyone will no where you are. If you turn it down you may not be able to hear or reply to the messages.
Airsoft, where nothing is hurt but feelings.