I used BBC from SDC to Madrid in June 2017.
I wanted to experience "all" modes of transport. Worked great. You subscribe and enter your profile and, if u wish, a photo (I sent a picture directly to the driver).
This allows you to view rides offered, the driver's profile, and past passengers reviews of said driver.
He said he posted the price at €30 for the 6 hour drive to Madrid from Santiago. (He was the cheapest) The posted price was €35 so the company's cut was €5 over his asking price. He doesn't get the money transfer until his passengers have entered their reviews. The driver also reviews his/her passengers.
One guy said he drives a lot for work and enjoys the company. A female driver only accepts female passengers.
The driver was a 35 y.o. airplane mechanic finishing a job and heading home. Passengers were a 38 yo female high school history teacher, a 23 yo male university student, and moi (71 yo female retiree).
It was fabulous. I'm bilingual so chatting the whole way was easy and fun. We stopped for lunch and ate as a group.
Drivers must put the drop-off location. Ours said he put Terminal del Sur (southern bus terminal) but said he was flexible as long as it wasn't too far out of his way. He dropped the gal off a block or so from her apt. The student and I got off at the Atocha station.
I would suggest that people with little Spanish write their profile in English with a sprinkle of Spanish.
I used Rome2Rio as the first search for travel options. Great app/site. It gives you air/train/ bus/driving/ and ride sharing, which sends you to BkaBlaCar! Each segment gives approximate travel time and costs.