The Str class has a noticeable performance improvement over gcc's
implementation of string in most areas. When comparing to
char*, performance is mixed, with Str coming ahead in some
cases and char* coming out better in others. I believe the main
benefit to Str is the stored length field that can
accelerate many operations. The advantage to char* comes in the
form of a simpler structure, direct compiler awareness, and a support
library that has been performance tuned over several decades.
As always, the best choice for a project involves a careful trade-off of
several contributing factors. I believe that the good performance, ease
of use, and high safety of the Str class make it a good option
for a number of situations.