Release Pool Singleton, Good or Bad?

Since I discovered Timur Doumler intervention at CppCon 2015
I’m using a release pool to avoid delete in the Audio Thread when I use shared ressources.
Would it be really a bad idea to make this pool a singleton to avoid going through all the hierarchy to pass it to far away clients ?
I heard a lot that singleton are evil but I’m not sure to understand why it will be such a bad thing in this case. After all this class ain’t going to change.
I really appreciate the help I’m new to programmation and wouldn’t like to start with bad habits …