A) Not particularly, it is first and foremost an option for users who want to switch between players and do not want the LMS running in their system.
B) That depends on a lot of factors. Both solutions run really well in our testing thus far. Both are based on librespot. If you just want to use one device, the Spotify Connect player might be preferable. However, for most users with multiroom ambitions we recommend the Spotty plugin.