Hi, I think most people prefer to use a whiteboard and marker. The first and most important reason of course is to understand that getting familiar with the online board is a whole new skill set for you to acquire while also preparing for your exam, which in my opinion is a waste of precious time. Then of course there is the question of usage - I took the test online on my laptop without a mouse, using the touchpad, and switching between your test window and whiteboard window is a nuisance. Also, drawing geometric figures on the online board was not easy for me and the extra time spent trying to get it right made me more stressed and prone to mistakes.
Get a whiteboard with a good quality dry erase marker and eraser. Practice using it a few times, and erasing will not take time at all. What I did was develop muscle memory and erase the board while reading the next question. DO NOT use a permanent marker. It has to be a dry erase marker. You cannot use any other pen with an eraser on the whiteboard. The blank/erased whiteboard must be shown to the proctor at the start and end of each section of the test, and when you return from the break if you choose to leave the room.