The whole 'gourmet' burger thing might be a fast food culinary fad that's reached its peak. It's when the vendors of these products reach large numbers that the tipping point tends to be close - Don't get me wrong, the premium burger will remain but it won't have the go-to consumer pull it currently holds... Remember the wealth of takeaway 'Mexican' shops, and even stand alone nacho shacks, of the 90's?
In the Christchurch market Fuel are up against Burgers and Beers, Velvet, Wisconsin and Red Box (probably others too... entry is quick and easy.) They're all pretty much working the same schtick - even Maccas has hit the gourmet button (https://mcdonalds.co.nz/create-your-taste.) Beyond that, all the gastro pubs now offer and aggressively market their burger offerings (Fox and Ferret, Cafe De la Mer, Engineers, Pedal Pusher...) The number of deals (especially - 2 for 1 - through online 'deal' sites, Facebook pages etc) suggests it's a difficult market to keep traction in. Unlimited NZ growth is not a given, and the degree of profitability from their new stores will be crucial.
The US situation is not one to gloss over either, they generated the 'overly optimistic price' with talk of 1000 stores in 8 years - 9 months on from that puffery they still have...none.
Tastes like a high risk proposition to me. GLTH.