The Topp twins are one of New Zealand's best loved comedy acts, and it's fair to say they're unique.

A pair of lesbian farm girls, they've campaigned over the years for gay rights and Maori rights and against apartheid and nuclear weapons through their signature mix of country music, dancing and yodelling.

Yes, that's right, yodelling.

It's unusual to say the least. And as their comedy-writer friend Paul Horan puts it: "On paper, yodelling lesbian twins don't really work."

But New Zealand has taken them to its heart, and this is the country's highest-grossing documentary film ever.

Director Leanne Pooley gives a revealing insight into the twins' life story, from their from days growing up to their breakthrough as buskers on the streets of Auckland and their subsequent sell-out tours.

They also spend excerpts of the film playing their cast of characters boozy farmers Ken Smythe and Ken Moller, posh socialites Prue and Dilly Ramsbotham and others.

But the problem is, I'm not from New Zealand and I don't really 'get' any of it. I can see how the twins with their wit and good cheer and complete refusal to fit in with convention have become popular. But their humour is so chock-full of cultural references and puns that anyone who is not from New Zealand is likely to struggle to understand it let alone laugh.

I found it difficult to make out what they were singing about in most of their songs and why their audiences were left rolling in the aisles. I did laugh out loud at a couple of their more risqué jokes although Bermuda's religious conservatives may not find them quite so funny.

The more serious parts of this film are moving and touching, particularly where the twins detail their involvement in the protest movement and how they've found loving relationships with their girlfriends despite being in the spotlight of fame.

Overall, I would recommend this to anyone with an open mind and a capacity to withstand a mixture of country music, cheesy puns and yodelling without running screaming from the cinema.

Otherwise, perhaps it would be better to give it a miss.

'The Topp Twins: Untouchable Girls', the Bermuda Underwater Exploration Institute, today at 8.30 p.m.