Loved Imerge. Purchased it 5 minutes ago, but oy!
Once you export one image from a project, say a PNG, the second you'd like to pick a different format, the software doesn't give me that option.
At a hunch, I opened up a new project and surely enough when I clicked export, the options came up the first time - but not the second time.
So it looks like Imerge Pro projects commit only to the format of the first export you make.
I don't think this was done on purpose.