Farrell started the first match against the Springboks last month but was dropped to the bench for the second and third Tests. England endured a 2-0 series defeat, drawing the third game, but Farrell has learnt much from the tour.
"The experience of playing in a series like that is what you benefit from most of all," he said.
"It's a massive challenge over there and we had three really tough games that could have gone either way.
"We can take a lot of confidence from that and the experience as a whole was totally beneficial. I didn't see any of the criticism of me. All I wanted to do was play and that pushed me on."