Yes, there are some advantages using this lib:
-Uses direct memory, instead of writing to the filesystem through /sys/class/gpio it maps to it's own memory memory the peripheral addresses and the access to these are done through raw pointers, so it should be much faster.
-Light, it only does the hardware manipulation, no extra checks, no validations, you must know what you do, but the final result should be more efficient.
-It uses Mono.Posix.Unix instead of declaring manually imports to the OS functions (what means if there is any change to these functions and you update Mono they will be handled).
-It implements the full PWM modules.
-It can work with or without root privileges, if you run it without root it can only interact with the GPIO.
-You can use RaspiSharp with it, check it at https://github.com/gusmanb/RaspiSharp
About the edge detector, you have two options, you can use the original functions on the bcm library (poll through bcm2835_gpio_eds) or the event detector inside the GPIO extras, the second one is the preferred method as it will not consume resources (no manual polling, uses system poll, which doesn't consume resources).
About speed, the bcm2835_gpio_eds should be as fast as the original C code except for the C# overhead, at the end it only reads a pointer, so it must be as fast as C# can be, the second method... well, not sure, haven't tested it, but it should be really fast as the library gets notified by the system when any IO is performed on the edge detection file.