I've been buying these for my business for years. We use them to sends check payments to vendors. The double window used to fit our pre printed checks perfectly but the last 2 boxes we ordered from Staples seem to cut off the vendor address and some of our payments are getting returned in the mail! Did the windows move up? Our check format has never changed so I don't know how to solve this problem.
The windows are too big and not in the right place for standard checks and these are not self-sealing. My mistake but I thought “gummed” meant they were. If they’re the right size for you and you don’t mind licking them they are fine.
They are a good quality and are consistent in the window dimensions. It takes a few seconds for the flap to stick so when doing a lot of sealing I press the flap against a damp cloth and then slide them under a medium weight book.