I asked the makers of Vignette about the fast shot mode and burst... Here's my response:
Thanks for contacting us.
The Fast Shot mode skips the preview and returns to the viewfinder so you can carry on taking photos as quickly as possible. Fast Shot also disables auto focus to make the photo taking as quickly as possible.
We have not, as yet, added a burst mode to Vignette. This is something we're hoping to do as soon as we can work out the complications.
In case you're interested, I recently used the Fast Mode at an air show which resulted in some great shots of moving planes.
Hope this information helps.
Kind regards,
Theresa