I used one when setting up my new (1 year ago) band saw. I put it on a fully tensioned blade and squared the tables miter slot to the blade. Worked great. I may have been lucky but the fence did not need any adjustment and I get accurate resaws deepest to date around 200mm.
Being a newbie to woodwork and having just bought my first bandsaw and about to set it up thought this might be a useful accessory, but then realized surely I can just use my mini magnetic spirit level and achieve the same thing?