It's been a while since I played with Services-For-Unix, but I recall it's better than Cygwin in that it's not a POSIX shim sitting on top of Win32, but actually sits beside Win32 on top of the NT kernel (which was always designed to support POSIX to some degree). It integrates the POSIX notion of user IDs with ActiveDirectory, etc.

Where it all falls down, of course, is the usual bane of proprietary unicies - packaging. I think there's a 'freeware' site with tarballs of various useful tools you can download, but nothing approaching even Cygwin's small and limited packaging and upgrade system, let alone a real distro like Debian.

It's much, much faster than Cygwin. Yes, it comes with most of the common shells out of the box: bash, ksh, etc. Even sets up start menu shortcuts for each, to encourage you to dip your toe in the water.

Most of the user-space tools are based on OpenBSD userland rather than GNU utilities. Like Cygwin, it uses PE-COFF for binaries. It comes with both real GCC and a GCC-like wrapper for MSVC so that you can attempt to build software without modifying existing build files.

Unfortunately, software compatibility isn't great. It's not that SUA/SFU is a bad implementation of UNIX, it's just that we live in a world where "everything is Linux." Building things on SUA/SFU really sucks, just like it sucks to build software on any other niche UNIX. (AIX, HP-UX, etc)