Rhinos this week completed the signing of the former Australia and New South Wales forward from Penrith Panthers on a four-year contract.
Merrin is Rhinos’ second marquee signing, after Tongan centre Konrad Hurrell, so part of his wages will be exempt from the salary cap.
He is Rhinos’ most high-profile recruit since countryman Danny Buderus a decade ago, but Furner believes he can still improve as a player.
At 29 he is coming to Betfred Super League at a younger age than many additions from the NRL and Furner enthused: “With middles and front-rowers they tend to play their best footy when they are 31/32/33.
“I think he has still got room to even get better.”
Merrin is set to arrive in England in around two weeks’ time, once paperwork has been completed.
Asked what he will bring to the team, Furner said: “Leadership. He is a very good professional.
“He’s an Origin player and he has played for Australia so he has played at the highest level.
“He is going to bring a lot of that experience to the team.
“He was with the Australian World Cup side last year and he has made it known he wants to play some really good footy.
“He is excited about coming to Leeds and about the way we want to play.”
Rhinos had been linked with Merrin since the end of last month, but it seemed last week he was set to stay at Penrith and there was also reported interest from other NRL clubs.
“I mentioned at my first press conference there’s been interest on both sides,” Furner added.
“It was just a matter of sorting out contracts as he was still contracted to Penrith.
“There’s been some to-ing and fro-ing from one end to the other, but I’m pleased it is all done.
“Gary [Hetherington, Rhinos’ chief executive], Kevin [Sinfield, director of rugby] and I have worked hard to get it over the line.”
Merrin will be the fourth new face in Rhinos’ 2019 squad, after Hurrell and half-backs Tuimoala Lolohea and Callum McLelland.
Furner confirmed Rhinos still have a vacancy on their overseas quota, but of the prospect of more signings, he said: “At the moment it is about getting all the squad together. We’ll see what’s needed positionally, if anything, at the moment.”
Pre-season training began for a group of 18 players last Monday and more will report back in two days’ time.
“It has been good,” Furner said of his first week.
“My job first is to build relationships with the current squad.
“They are training a bit differently to what they are used to and there’s a lot of young players there including some who’ve not played first grade and are getting their first taste of training.”
At the other end of the scale, 32-year-old Carl Ablett has signed a new two year contract and Jamie Jones-Buchanan, 37, will have a final season in the squad.
“There’s no doubt they can contribute,” Furner said.
“Look at JJB, he is a total professional. Looking at some of our testing in the first week he was one of our leaders. That says a fair bit for him.”