What's the difference between the Source™ and Big Brush™/Flex™ Brush?

The Source™ handle is straight, not angled like the Big Brush™ and Flex™ Brush, and the Source™ handle is made from recycled materials like dollar bills, wood, hemp, coconut shells, starch, or recycled soda pop bottles. The Source™ is sold with Replacement Heads which are 50% smaller than the  Big Brush™ and Flex™ Brush heads (however you can use the Big Brush Replacement Heads with the Source). The Source™ can be either right or left handed depending on how you put the Replacement Head into the handle. The  Big Brush™ and Flex Brush come in right and left hand versions.