https://www.videotoolshed.com/product/make-transcriber-files/ - $25 Mac or PC
I do not work for VideoToolShed but Bouke, the developer, programmed this utility for me and I told him it could be useful to other sound mixers and they should put it up for sale to the public. Apparently it is now available!
It's a fast and simple utility and has some nice features for us. You select the source folder for your BWFs (can manually or automatically detect frame rate), an output folder where you want the MP3s to go, check the boxes for which track or tracks you want included in the mono mix and hit create. It makes the mono mix for you so even if you only recorded isos you can still make a mono track for transcription. Does the conversion super quickly and makes nice and small MP3 files.
I originally wanted this so that I didn't have to give up a CF or SD slot in a Sound Devices 6-series for MP3 recording. It's also handy for Zaxcom users if you don't have the MP3 option.
PS.. the resulting MP3 should have TC info in the metadata just like sound devices does it..