One concern was not only who can take on Prime Minister John Key in the public appeal stakes - a contest Shearer would win - but who will defend Labour's own turf in the crowded campground that is the Opposition.
Winston Peters' NZ First and the Greens are both significant forces and will suck up a lot of air. This draws people to Cunliffe because of his experience in the political battlefield of the debating chamber - the importance of which is often underestimated but swiftly learned.
And, despite Grant Robertson's claims that he can "best any of the National front bench in Parliament," that lack of experience in Parliament is the big hole in Shearer's current combination.
However, there are counterbalancing concerns about whether Cunliffe would alienate caucus and about his public appeal.
In an attempt to reassure MPs about his, Cunliffe is now making repeated references to "reuniting caucus" and working as a whole team.
The advantage for Cunliffe is that he has had months to work out his plan for the party. He can now go to caucus and tell them exactly what he is planning. Shearer's last-minute bid, on the other hand, has left him unprepared.
For some, Shearer's greatest virtue is that he is not David Cunliffe. Other than that, nobody knows exactly what they're voting for. He is effectively asking his colleagues to vote for him on faith and reputation - and a willingness to take a risk. As one of the MPs said, there was little to lose.
That caucus will be expecting that Shearer's foibles - most notably a tendency to falter when speaking - will be relatively easily ironed out.
Cunliffe has taken aim at Shearer's campaign, saying on Q+A that the support of Goff and King was a liability for him. The intention was clear: to make Shearer look like a puppet of the old leadership.
Whether by accident or design, Shearer's consistent refusal to select a deputy or offer positions to MPs could help dispel this.
He could be resisting a ticket in case bridge-building between the two camps is needed, in much the same way Helen Clark anointed Cullen her deputy after the failed attempt to get her to stand aside. Either way, it is a promising sign that Shearer, regardless of his clumsy speech patterns, has some mettle.
It could backfire on him - many MPs will be weighing up what their prospects are under the two leaders and Shearer has surprised some by his refusal to play the game of portfolios for votes.
However, so far many have been willing to take that risk. At last count, he had about 16 committed supporters. Cunliffe was on about 10 and some of those were uncertain. Cunliffe will need every one of the eight undecideds to win. Hope and fear, indeed.
