Alonso caused a huge twist in F1's transfer market last summer by signing a deal with Aston Martin, leaving Alpine after two seasons.
Ahead of his 19th season in F1, the 41-year-old has looked as hungry and ambitious as ever, hoping his decision to jump ship will pay off as the AMR23 looked promising in Bahrain testing.
According to the team's tech chief Fallows, Alonso has injected his new team - his sixth different outfit in F1 - with energy on his arrival.
"He is clearly a very impressive chap; he is incredibly motivated, incredibly competitive and he’s brought a huge amount of energy to the team," Fallows said.
"He has been very impressive from the moment he got in the car last year and his feedback is where you expect it to be for somebody with his level of experience.
"He has the ability to diagnose issues with the car in a way that we, as an engineering team, are very, very pleased with."
In Alonso the Silverstone team has attracted another world champion to replace the retiring Sebastian Vettel.
While Fallows acknowledged the two are "different", Alonso's enthusiasm is infectious for the entire operation.
"They are different people, for sure," Fallows said. "But I think you know Fernando's still got a huge amount of energy.
"He is still very, very keen to go racing and he keeps saying that he’ll just carry on as long as he can possibly go, so that’s very infectious.
"It’s been great for the team to come round and say hello to people. We have various Spanish members of the team as well, who were incredibly excited that he’s arrived. So yeah, it’s been great having him onboard so far."
Aston Martin's pace during winter testing caused quite a stir in the paddock, with Alonso's long-run pace suggesting that the team could mix it up with Ferrari and Red Bull, but according to Fallows there were too many variables to draw solid conclusions.
But Alonso and team-mate Lance Stroll did look competitive again in Friday's FP2 for the Bahrain Grand Prix, which was held in similar night-time conditions encountered during qualifying and the race.
Alonso finished top after demoting Red Bull's reigning world champion Max Verstappen by 0.169s.
Stroll finished sixth on his first day in the car after missing testing due to a wrist injury, which ruled out the Canadian from last week's pre-season test.
