bweinfach ticket with bus?

I am planning to go from stuttgart airport to tuibingen rn, so I was looking up in the db app for a travel option.
When I searched, the fastest and the nearest travel time was taking the x82 bus, so tried to buy a ticket until I saw bwEINFACH ticket saying, unrestricted choice of local trains on the day of travel.
Other options were seasonal or monthly passes, so I think I have to buy this, but the description not including the bus option made me question.
Should I buy this or should I just find a another way?