Sessegnon struck the opener against former club Sunderland in WBA's 3-0 rout.
Ridgewell believes Sunderland's loss of Sessegnon is his team's gain, saying: "He's a quality player.
"We saw that at Sunderland and getting him here is obviously good for us.
"Hopefully he carries on the way he started and that can only be a bonus for us.
"To get that kind of quality to the club is great and it's a coup for the club to get him."