I would say that investing in open source software is never time loosing. As the software does not depends on editor good will but on community people. That's a great difference as invested people can change without loosing the software, improvements can be proposed by anyone, ...
That what we did with GrandOrgue and the software has known so much improvements for three years.
But, at the end, it is your choice to use the one that fits your needs. I would say I use (not intensively) Musescore and I'm really happy with it (available for Linux/Windows/Mac).
My two cents