The cost is good. The address windows are sized oddly for my three part checks. The memo line shows through the window and this can confuse postal system equipment when they read the zip code.
One corner on the inside of the envelopes are stuck together a little bit just enough that the check doesn't slide in the envelope evenly. Only used about a 100 of the envelopes but it seems to be an issue on the majority so far. Envelopes still work it is just annoying.