David Flatman: American Manoa has made biggest impact this season

My wife drives a German car and, frankly, treats the thing like a wellington boot. It does not get cleaned or serviced and it is never less than six inches deep in used baby wipes and morsels of organic infantile snacks.

But it never breaks down, which makes me wonder what the Germans could achieve if they ever thought about giving rugby a proper crack.

It is a terrifying thought, but not quite as bad as imagining where American rugby might be in a decade should someone with a few dollars and a lot of vision decide to take the job on. A million miles away from being a national sport, rugby in the States is still producing the odd top-end player.

The American international winger Takudzwa Ngwenya is a star in the Biarritz side – yes, he was born elsewhere, but who worries about that these days? – and Todd Clever made a splash in both New Zealand and South Africa, where he played for the Lions. He now plays in Japan in the Top League, where the biggest salaries are to be found.

Now we have in our midst a new American star. Samu Manoa is, to my mind, one of the very best overseas signings by a Premiership club in recent years. Harlequins' Nick Evans might top that list, but give Manoa time and I think he might achieve – albeit with fewer points to his name – the same level of respect in the league. I do not mind admitting I had no idea who he was when he arrived – but I know now.

There are plenty of players who can carry a bit of ball, who can collide with venom and who can catch and pass too. But actually there are very few who seem able to do all three repeatedly without seeming to suffer from fatigue or broken-body syndrome. Manoa arrived at Saints as a big unit with an easily mispronounced name (think Manu Samoa), but I think he is now their most valuable player. Tom Wood does massive amounts of work and Stephen Myler doubtless makes more tough decisions during a game, but the big American is that very rare commodity, a high-impact, high-work-rate player.

Sébastien Chabal had a big impact, certainly, but his work-rate was negligible. Chris Robshaw's work ethic is unarguably stunning, but he is rarely seen melting opposition players in the tackle.

Manoa has the power of a Chris Hala'ufia and seemingly the durability of an Alex Brown. He plays lots of games and lots of minutes but, as I watched him bullying one Saracens player after another last week, he just did not seem to get tired. I spoke to one of the Saracens after the match and he described Manoa as "a serious piece of meat – brutally strong". So he is a special specimen, but this does not make him a good rugby player.

What makes him a good player is his enthusiasm to carry the ball in a wonderfully direct manner, forcing invariably smaller men to tackle him instead of offering them a jersey to grab as he tries to skirt around them.

He has good skills, too, so the ball is regularly shifted and, with tacklers hanging off him, the point of attack is altered. Without being terribly quick, he is a real attacking weapon.

His game is not complicated and he seems simply to enjoy bashing around, but when the moment comes he is as explosive and threatening as anybody in the country.

His tight work is equally impressive; as I watch him mauling and scrummaging I see a player trying like hell – and only Tom Youngs hits rucks with more outright spite. This may sound non-negotiable as a professional, but often I look at rolling mauls and watch the legs and feet of the men involved. Some are pumping and tearing at the turf while others are more relaxed, perhaps waiting for someone else to generate the momentum.

Manoa's way is to graft, even when he thinks nobody is watching, and this, as well as the sheer brute force he so reliably displays, is why I think he has been the player of the year.