Loanees Whiteman and Kongolo both netted in the Carabao Cup win at Bradford City on Tuesday.
Left back Andrew has also slotted in seamlessly since his summer switch from Grimsby Town.
Speaking ahead of today’s trip to Blackburn Rovers, Ferguson said: “I’m not surprised, I’m pleased. They’re quality players.
“They’ve done very well. It’s important they bed in quickly and it looks like they’ve been here for a while, and that’s a credit to them.
“The fact we got Ben, with him being a loan player, at the start of pre-season was important so he knew exactly what to do tactically.
“So I’m not overly surprised, just pleased. They look really important players for us.
“When you recruit you don’t know how it’s going to work out but you want them to be consistent throughout the season.
“When you bring players into the club you do it for a reason, to try and improve the squad.
“They look like they’ve improved us.”
Rovers travel to Blackburn in good spirits, unbeaten in their opening two games.
“I think we’ve looked fairly solid, we can be a bit more solid,” said Ferguson.
“And we’ve looked very good going forward, in different systems.”