I use these pens for work and they are great. Looks just like normal ball point ink on paper but can be removed with friction. They include an eraser on the tip like a pencil.
These pens are normally a couple of £ each, so a full pack of 12 assorted pens for £3.50 is an absolute bargain. The pack includes 4 roller balls, 1 green, 1 black and 2 blue, 4 highlighters of assorted colours and 4 fine point pens, blue, black, green and red.
I picked mine up at Asda Gosforth where they had loads of packs, they also had loads of other stationary heavily reduced.