I don't see why the post office would have any issues with it since they lie flat. And, I'm sure it will save you lots of time!
If you're gonna do 150 of these, I'd modify the process a bit to make it run smoother. After printing, I would score the entire page at the spot where it's going to wrap around the envelope. And instead of adding glue to each strip, I would run the page through a Xyron and then cut them down to size.
HTH