I use this when marking my starter flasks. I brew a lot, so I often have multiple starters going at one time. This product allows me to keep my starters straight. It washes or wipes off easily and seems to last forever!
I use this to mark up my Erlenmeyer flasks when making starters. When brewing for competition, I usually have multiple starters going at once, so this handy tool keeps me on track with what goes with what.
The only challenge is keeping a good point on it so your marking doesn't messy. I don't have the greatest handwriting, so it's probably just me!
I use this china marker to write dates on bottles and carboys. This may seem like a no-brainer, but be sure the surface you are writing on is clean and dry or you will have some issues applying a readable amount of wax. Removing the wax can be tricky but a slightly abrasive pad will take care of it.