[Andy Neil] “Unless the .png is smaller than the project size, there won’t be a noticeable difference in the masking of the frame. However, a mask effect is much more adjustable.”
Also, a problem I forgot to mention when using the letterbox effect – is that you can’t make adjustments on the footage that doesn’t affect the letterbox. So, for example, if I want to scale some footage, that will affect the letterbox as well. Unless there’s something I do not know of, this can’t be adjusted.