Well a few facts (and I'm not spark fanboi)... Spark still have something like 43% of the broadband market in NZ and thats the largest RSP (retailer) of fixed line broadband in the country.
Chorus (as one of the 4 fibre companies) are still installing their part of UFB and are on track to finish their part of the network and make streets "fibre ready". This should be by 2019 but the other fibre companies have completed their (very much smaller) builds already. So when an order comes in from a customer, there is still a bit more work to blow the fibre through the ducts and do the build on each property (be that residential or business). What Spark and UFF are doing is trying to do the final "customer build" part en mass for a street as UFF have completed their slice of the underlying UFB network around the Hamilton / Taraunga area.
Chorus have 70% of the UFB build and a lot more complicated install issues like multi dwelling units and power pole sharing problems. UFF and Northpower (two of the 3 other fibre companies) are power companies so have used their own poles to help build UFB nice and quickly for their regions of NZ.
The irony about this push from Spark is they want to migrate customers off copper (one Chorus asset that is being sweated rather nicely for the share holders) and either onto the UFB product (hello more Chorus / other fibre company income) or away from the rented infrastructure and onto their own 4G network and (I'm guessing here) even more revenue per user as no line charges for retailing the fibre product are incurred.
I think its a good thing the en mass street install. If UFF were savy and Spark agreed, they would get all the other RSPs to do the same street, so the likes of Vodafone, 2degrees and Vocus would rock up as well with their customers and migrate the whole street in one go.