Matavesi has played twice for the black, green and gold so far, helping them to secure back-to-back Premiership Rugby Cup wins, against Saracens and Newcastle Falcons.
The 26-year-old, brother of Saints hooker Sam Matavesi, possesses plenty of power and adds a different element to the centre mix at cinch Stadium at Franklin's Gardens.
And attack coach Vesty has certainly been happy with how the former Ospreys and Newcastle Falcons back has been doing.
"Joel's been coming along really well," Vesty said.
"He came to us after having a bit of time out from playing rugby and he decided he wanted to get back into it.
"He came in for a bit of a trial and he's worked really hard.
"His body shape has changed, he's become more athletic and I've been really impressed with how he's conducted himself on the training pitch and also when he's had the chances to play for both Bedford and for us."