I see 2 major flaws: 1) They are THIN. You do see the check through the envelope. . 2) Keep in mind: the address window for checks is LOW on the envelope. Therefore it shows BOTH the address AND the memo section of the check through the window. I don't think a window envelope for a check should show the memo section. We use QuickBooks check stock -- nothing fancy. Since it was not what I was looking for they are being returned. So I can not evaluate their sealing qualities. Will try another type with security feature and a higher window.
I use these envelopes on a daily basis for our payroll to go out in and they have never disappointed me. They are a great price for getting so many in a box.
One would think that all envelopes are the same but that is very far from the truth. These envelopes work perfectly for paychecks vendor checks or any checks. They are the perfect size and the glue on the envelope flap is palpable. In the past our company has used many different brands of envelopes but Staples #9 with a left window are perfect for any check application that you might have.