Similar vehicles are known as rickshaw in Africa and Tuk-Tuk in Thailand. Bajaj seat two passengers comfortably and up to five passengers - depending on the size of the passenger of course. Their areas of operation are limited to one mayoralty in the city. Jakarta Barat, Jakarta Pusat, etc. The drivers are not allowed to go out of their area and aren't allowed onto many main roads, so routes may be a bit circuitous.
Fare determination is by bargaining.
It's always best to ask an Indonesian what they would pay for a trip to a particular destination from your point of departure, and then bargain and pay accordingly. A ride in a bajaj is hot, utilizing AC alam - or nature's air conditioning. My favorite maneuver is when the bajaj driver decides to flip a u-turn in the middle of the road. There is some protection from the rain, unless it's blowing hard. You'd think you'd have to be careful about robbery since the vehicle is so open - but it's not as common as robberies in buses.