Mako and Billy Vunipola have helped Saracens become a "more complete side", says Clermont hooker Benjamin Kayser.
Younger Vunipola brother Billy was reunited with his sibling when he joined Saracens in the summer, with the two having previously played together at Bristol.
The powerful running of number eight Billy, 21, and prop Mako, 23, has helped Sarries to the top of the Aviva Premiership table and a certain home fixture in the play-off semi-finals.
They have also reached the Heineken Cup semi-finals, where they will face Kayser's side, who beat them 22-3 in the last eight of the competition in 2012.
However, Kayser believes the French side are in for a much tougher game when the two meet at Twickenham on Saturday.
"There are a few key changes in their side since our last meeting; the influence of the Vunipola brothers is huge," said 29-year-old France hooker Kayser.
"Chris Ashton has joined the party, and I just think they have got a lot more threats in their ball-carrying.
"They still have the same style of rugby, they are very clinical, very well-organised, their strategies are well in place.
"And it's probably the most physical rugby there is to play, in terms of intensity and the number of phases that they are willing to go through to put the defence under pressure.
"So I think that's where they are really, they've got threats everywhere, either forwards or backs, I just think they are more of a complete side than two years ago."
Kayser also admits his side will need to subdue former England captain Steve Borthwick, who will be looking to secure Europe's top prize before he retires this summer after 16 years of top-flight rugby.
"When you speak about a player before a game it's usually quite good for his reputation and shows his influence," said Kayser.
"Anyone who knows rugby knows that a key lock like that, captaining England, he's not just anybody.
"He's a very important leader for them, and it will be important for us to put all their leaders under pressure to make sure that we win the battle."
You can watch Saracens v Clermont Auvergne live from Twickenham on Saturday, Sky Sports 2HD at 3.15pm
Who will contest the Heineken Cup final?
Toulon and Clermont
Saracens and Munster
Clermont and Munster
Toulon and Saracens