This is the first (trial) dev branch release of PTVS! Previously we only released at the standard Alpha/Beta/RC/RTM check points. However some users would like to have access to more recent bits earlier. The dev branch builds address that need. We're hoping to do these approximately every 2-3 weeks.
Note that you can always build PTVS from the latest sources yourself. Link for instructions: https://pytools.codeplex.com/wikipage?title=Build%20Instructions%20for%20PTVS
These downloads have been signed, virus scanned, etc. However being from a dev branch, have not gone through extensive testing.