I'm not a New Zealander, but having lived there for the last four years while studying in the university, perhaps I could say something about this. Like Australia, all of New Zealand's top players ply their trade in European/US leagues; we know of our Ryan Nelsen and Simon Elliot of Fulham, I believe there are one or two kiwis in the Dutch and German leagues. There are also a few in the MLS or playing college football. In the four years that I was in New Zealand, the All Whites reached the peak of beating Australia (although it was a purely locally-based Australian team) in the Oceania Cup and went on to represent Oceania in the Confederations Cup. After that however, they lost to Samoa (or was it Tonga?) in World Cup qualfication (completely unheard of...before Australia left to join the AFC, World Cup qualification in this region was always a two horse race between Australia and New Zealand) and have been in a state of depression, especially with the New Zealand Knights being so rubbish in the A-league.
The last I saw the All Whites play was a two game 'test' against Malaysia in New Zealand earlier this year. The kiwis won both games very easily (having said that Malaysia isn't exactly world class opposition) and in my opinion they are a very physical side without much pace or creativity. Think of a team of Robbie Savages, lots of stamina and enthusiasm but not much in terms of pace or flair. In the games against Malaysia, their best player were the wingers Vaughn Coveny and Jeremy Brockie. Their captain when Nelsen is not playing is Danny Hay, who used to play for Leeds and is now the captain of the New Zealand Knights (did I mention they are rubbish?).
I have not been following their results in their tour of Europe (among other teams they played Brazil before the world cup! Nelsen was supposed to play but at that time was recovering from a broken leg) but this is clearly not Rovers' toughest friendly fixture. Perhaps however, it is suitable preparation for the Rovers, after weeks of European opposition, this game is to acclimatise the players back to the more physical British style of play.
Because this friendly is so close to the start of the season, anything less than a comprehensive victory against New Zealand (with or without Nelsen) would be worrying.