The former Liverpool and Tottenham striker has praised the duo for helping out in defence despite being attacking players.
Brazil international Firmino, 26, can operate as a forward or as a winger, and so can 25-year-old South Korea international Son.
Crouch wrote in The Daily Mail: “Football has altered dramatically due to the relentless workrate of men such as Firmino and Son Heung-min of Tottenham, who is one of the top players in the League. He would improve any of the best teams.
“These are forwards who won’t stop. Look at Firmino. He is a top goalscorer, but the thing that blows me away is what happens when he loses the ball.
“Straight away he’s on his feet and gets it back. He must be an absolute nightmare for defenders to handle.
“It says everything about how much he runs that he’s covered 165 miles in the Premier League this season. It’s the same with Son (129 miles), who is so underrated.”
Firmino and Son are two of the best attacking players in the Premier League and are hugely important for their respective teams.
Mohamed Salah may be hitting the headlines for Liverpool this season, but the importance of Firmino cannot be underestimated.
The Brazil international, who cost Liverpool £29 million in transfer fees when they signed him from Hoffenheim in the summer of 2015 according to BBC Sport, has scored 13 goals in the Premier League and seven in the Champions League so far this season.
Son, who earns £60,000 per week at Spurs according to The Sun, is also in great form for Tottenham this season, having scored 10 goals in the Premier League and four in the Champions League.
Spurs signed Son from Bayer Leverkusen in the summer of 2015 for a transfer fee reported by The Guardian to be worth £22m.