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.”
Farrell was speaking at Saracens’ new home ground at Barnet Copthall Stadium in north London, which is to be renamed Allianz Park.
The club agreed an £8 million, six-year deal with Allianz that secures the German financial services provider stadium naming rights and shirt sponsorship.
Saracens hope to move into their new home in Hendon in February following a 15-year tenancy at Vicarage Road.
Watching their team at the home of Watford Football Club has not always been appreciated by the Saracens fans, but Farrell is adamant that he will retain his fond memories of the stadium.
“Vicarage Road is the place where I broke into the Saracens first team and I spent my first two seasons there,” he explained.
“We won the Premiership while we were playing there, which was a privilege.
“It’s a pitch where you play rugby, it doesn’t really matter what’s going on around it.
Farrell is broadly optimistic that the club can go from strength to strength.
“Although attendances weren’t what we hoped, we’re looking forward to the future and getting into this place. Having two home grounds this season won’t be a problem. Hopefully we’ll turn this place into a fortress and attendances will build and build,” he said.