if used correctly, you should have nothing to fear. i have used one for 10 years [not all the time, once or twice a year] and the only time anything negative happened was when an inexperienced friend yelled at a spirit. she wasn't attacked, the spirit just stopped talking and refused to continue until my friend apologized and stepped out of the circle.
i feel you need two people to work the board. in my coven we do it blindfolded to make sure people aren't messing with the board, and a third person reads and records answers. when you use a board, cast a circle to keep negative beings out, meditate and clear your mind, and try to keep in a calm state. once you are done, thank the spirit, say goodbye, open the circle, store the board in a safe place, and cleanse the area just as a precautionary. i usually leave the cleansing until the day after since we typically use the board on Samhain and we welcome wandering spirits to stay the night. if in the morning the spirits decide to stay, then we cleanse. if you feel safer doing so right after, you can, theres no law against it.