Struggling with their home form and facing the prospect of relegation when the two players arrived, Sheffield have gone on to comfortably make the play-offs.
They also beat Batley in their first elimination play-off at the weekend.
“Etu has been outstanding, and Briggsy as well,” Aston told Love Rugby League.
“Both have come into the group and been outstanding. You don’t play at the level Etu has played at and not have quality.
“He’s been great, and he’s a player who wants to play, and plays with a smile on his face.
“It’s the same with Kyle. When I was at Featherstone the other week, they were saying to me, ‘What have you done to Briggsy?’
“I haven’t done anything to him, he’s done it himself. He’s got a smile on his face and he’s enjoying his rugby – and that’s the key.
“Both have been massive for us.”
Aston admitted that, while he was pleased with his team’s defensive effort against Batley, the team did not flow in attack as he would have liked.
“Over the last month or so we’ve been playing some great rugby,” he added.
“I want to play with tempo, I don’t think Batley allowed us to play with tempo. I thought it was niggly and there was lots of messing about in the ruck, which didn’t get cleaned up.
“What we have done is blast teams away in the last few weeks, but we had a bit of sluggish start.
“It’s still a bit of concern, but we’ll address it.”