What are the significant memory and GC differences between Visual Studio's hat operator and C++ shared_ptr?

Aside from cross-platform, cross-compiler compatibility, what are the significant differences between Microsoft Visual C++ (C++ Component Extensions) Handle to Object Operator (^) and C++ 11 std::shared_ptr?

Both seem to support automatic garbage collection through the use of reference counting and I would assume require some additional memory to track this information. Is this extra memory overhead significant and does it differ greatly between the two implementations?

Additionally, are there ways to manage when the garbage collection occurs in either the MS C++ Component Extensions or C++ 11 environments to prevent stalling at undesirable times?

MSDN Documentation: Handle to Object Operator (^) (C++ Component Extensions)

C++ 11 smart_ptr: std::shared_ptr