Cassini is not legal as far as we know. It's just a hack up of GiriGiri and although we won't censor discussion of it, most of our members make a choice not to provide support/help to people who use it.
Giri may have been good, and running full speed, but it has several advantages in its favor. Sega has intimate knowledge of how their consoles work and all the hardware schematics they need to study when translating its functions into a software program. They also have the luxury of porting any code / functions to their software emulator such as the Saturn BIOS and other ways of doing hardware functions that others may not have the rights to legally use code for, etc.
Other emulators are legal because they have to reverse engineer the console, in a way that it does NOT work like the original Hardware (again Sega is not restricted by that because they own all the rights/copyrights). Reverse engineering all by itself is an extremely expensive and time consuming effort by a corporation - let alone one or more open source programmers doing a project in their spare time. It's a matter of knowledge, skill, and time, to develop any emulator.
However, I believe Steve Snake (the programmer behind Kega Fusion and its earlier incarnations) is going to be the savior of Saturn emulation - whenever he finally gets around to putting out a finished, stable project, or incorporating that code into Kega Fusion or whatever he plans to do.
Steve obviously has great skill and knowledge, and worked in the games industry for many years, especially around Sega hardware (which is why his stuff is so good and accurate). Many months ago he dropped me an e-mail link to a Video of Burning Rangers running at full speed WITH sound. It was captured from his PC via TV-out and was a little stuttering but he assured me that was because of the capture process, not the emulator itself.
That gives me a little hope.. Although I have not been able to demo the program or anything (getting an e-mail / reply from him is like winning the lottery at times) I have faith based on his success with Kega Fusion, that whenever he gets around to adding Saturn support, or releasing an independant program - it is going to rock and kill everything else out there, including SSF.