Plus points - they're chalk markers with brilliant colours to choose from.
Minus points - you need industrial strength products to remove them from your chalk board! I tried all sorts of household cleaners but the only product that eventually worked was Bar Keeper's Friend. After a long rub with BKF and lots of elbow grease the colour does come away but you are left with a feint 'ghost' of what has been written, still intact in certain lights. I have a lovely, quirky chalk board clock which was chosen because we can write notes on it whenever the need arises. Unfortunately, the beauty of the clock has now been marred with 'ghost' images of past notes because of these markers. The markers look beautiful in the way you can write and manipulate them, as opposed to ordinary, messy chalk but the downside is a huge price to pay. My clock is now ruined! Stick with ordinary chalk.