The 21-year-old, who joined on loan in January, scored his sixth and seventh goals for Blackburn in Saturday's 3-0 win over Blackpool. Armstrong also won League One Player of the Month for February.
"He's a special player with the ability to hurt any team in this league," Smallwood said.
"He's on fire at the moment, player of the month, and hopefully that continues.
"The lay-off to Adam was great - it had the perfect weight on it. The finish was brilliant.
"If he can continue as he has done for the remainder of this season then I think we'll get the job done."
He added: "He's a very good professional, a quiet lad but he's mixing in well. He does his talking on the pitch and hopefully that can continue. He can help us this season.
"He's a striker but is scoring goals from the left wing.
"He makes it look easy with the positions he takes up.
"He's a natural finisher, and Danny's the same, but Arma's showing he can do it so early on in his career."