His phrase of the moment is "you betcha" - frequently spouted when he is asked if he intends to take action on something close to Labour hearts.
He has busted Labour out of its self-tailored straitjacket of trying to be all things to all people, a strategy which ended up satisfying no one.
If breaking Labour free from its shackles and thrusting it leftwards has upset some people, so be it. Cunliffe probably deduces that, in most cases, those complaining are vested interests who benefit from Labour not deviating from the status quo.
This Cunliffe has not been so much a breath of fresh air for his party, as a gale of enlightenment who has refilled Labour's ideological sails and got the party moving forward again with a fair degree of unity.
Labour is starting to believe in itself once more. And that should worry National.
Then there is the other Cunliffe. This is the slightly too brash, but still decisive-sounding version who - when his statements are subject to scrutiny - leaves the listener none the wiser as to what he really thinks and where he stands.
This is Cunliffe the professional politician who either refuses to or cannot give a straight answer. Instead, the listener is served up rhetoric and bluster.
The straight-shooter persona could be Cunliffe's making as a leader of real stature. That persona must prevail if he is to have any show of beating John Key next year.
The duck-and-dodge persona threatens to be his undoing, leaving the impression that, beneath the surface gloss, he is just another politician, albeit a very clever one.
The first Cunliffe was much in evidence on Wednesday at a public meeting at Victoria University, where he was asked to articulate his vision for Labour.
During his half-hour address, he talked about ensuring the wealthy pay their fair share of tax, saying the burden was falling disproportionately on middle-income earners.
He announced that a government he led would review the law covering trusts and other tax-avoidance mechanisms - "no ifs, no buts, no maybes".
Admittedly, this was an easy target for Cunliffe, but it was all solid Labour tub-thumping stuff. It was another small signal that any government he runs is going to be a very different beast from the last Labour administration.
Wednesday's on-campus performance contrasted markedly with his speech in Parliament the previous day during the final reading on the legislation approving the contract between the Government and SkyCity under which the casino company will build a convention centre in Auckland in exchange for an extension of its casino licence and more gaming machines and tables.
Here Cunliffe has fallen prey to a plethora of ifs, buts and maybes. The proposed convention centre is an extremely ticklish problem for his party. The caucus is clearly split between those MPs who want to take a moral stand on the social cost of gambling and those who see the project as an example of the kind of job-creating investment Labour should be welcoming with open arms.
To complicate things, the Greens are hovering in the background promising to rip up the contract, thereby increasing the pressure on Labour to do likewise.
Labour already has its work cut out convincing voters it would be a responsible manager of the economy without being lumbered with the perception that it might ride roughshod over a contract without paying compensation, and could yet do so.
Although the agreement between the Government and SkyCity is unlikely to be replicated, Labour's opponents would paint any reneging on the deal as scaring off foreign investors and revealing Labour to be a poor economic manager.
But the Labour leader seems to want to have it all ways. He told Parliament that Labour - if it won power - would not "dynamite" a half-built convention centre. Neither would it rip up the contract . Yet, Labour reserved the right to review the contract, particularly the number of gaming tables.
That would still amount to breaking the contract. But Cunliffe says Labour is not guaranteeing that it would pay compensation.
The impression from Cunliffe's remarks inside and outside Parliament is that he is talking tough on the SkyCity deal before next year's election, but is also hinting that when push comes to shove, Labour would abide by the contract or demand cosmetic changes at most.
Watching all this unfold, the Greens are heartened by what they see as a tougher stance on Cunliffe's part even though it seems he does not intend holding himself to it.
Whether they can force him to scotch the whole agreement if the two parties are in coalition simply depends on how much leverage voters give the Greens. Tearing up the contract will be on the coalition negotiating table, but will not be a bottom line for the Greens.
There is another reason why Cunliffe is talking tough on the convention centre agreement, however. Part of his overall strategy is to try to paint Key as someone who is only concerned with looking after the interests of National's big business mates and leaving those on middle incomes downwards to fend for themselves.
Cunliffe is trying to develop in voters' minds an "us versus them" mentality that he hopes will ultimately turn middle New Zealand against Key and National.
To stoke that fire, Cunliffe has sought to remind people of Key's close contacts with SkyCity.
In Parliament, Cunliffe referred to the "wide boys in their alligator shoes" from "the big end of town" getting preferential treatment from National.
It is colourful language. But the voters can see the quandary that the convention centre poses for Labour. It is a choice between jobs and stimulating the Auckland economy or sitting on the moral high ground and feeling good about yourself. It is not difficult to determine what the best option is for Labour.
Rather than playing games with semantics, the politically wise thing for Labour to do would be to express its unhappiness with the SkyCity deal, but accept it is a fait accompli.
That is what the the first Cunliffe would do. But is the second version listening?
