If you have the capability to emulate on a PC, you will get a vastly superior visual and performance experience (often running flawlessly at 4K/60fps). If you are restricted to a hacked Switch, the "gratis" download is technically functional, but you are playing a compromised version of a very good game.
Downloading copyrighted game files is considered copyright infringement and is illegal in many jurisdictions. Official Ways to Play Sonic Superstars
Sonic Superstars Platform: Nintendo Switch Format Analyzed: Switch NSP (Unsigned/Downloaded)
Enjoy the 2D platforming feel with fully 3D graphics.