Pro Similar to OSX
Etoile is built on GNUStep, which is derived from OpenStep which in turn was the open source alternative of NeXTSTEP -- the same one on which OSX was built on.
All of this makes it very similar to OSX, making it possible for OSX users to feel right at home using it. It may also further improve interoperability between Linux and OSX.
Con Hard to get running
There are no official packages for major Linux distros so users have to compile it from source, which is not inherently hard but difficulties in setting it up have been widely reported, especially for Ubuntu.
Con Slow development
Etoile is not very popular. This means that there are very few developers working on it at a very slow pace. This could be a problem for people who want constant releases and new features.