Hey.
First up...This is "Norwegian" and not "Norwegian Cruise Line".
These two have absolutely nothing to do with each other.

...
The Fact :
They started this "Try-Out" to MCO in May 2014.
Remember,this is a "low cost" carrier.
That mean that unless you pay,you will not get any food/drinks or checked in baggage on this 12 hr flight (10hr return).
...
The Good :
Brand New Boing 787 Dreamliner w all the standard perks...like a bunch of movies/3Dmap etc.
The prices are rely good (sept 2014,about 170-200$ one way...that is osl-mco direct.i dont know the price from U.K)
We (i) are Norwegians,so we have an overall good quality and service. This is not Ryan Air
And yes...more planes are comming,and Norwegian Airlines are the largest plane buyer in the world,from Boing,in 2013.
...
The Prob :
Norwegian ONLY have 2 (TWO) long range airplanes.(2x787).
These are switch on routes to Asia and US.
If 1 have a mechanical issue (OMG,there have been LOTS of that for them),then they have no replacement aircraft,and you are "stuck" where you are until your plane comes.
...
Enjoy these official info videos from them.
https://www.youtube.com/watch?v=1uB3-KESNKk
and
https://www.youtube.com/watch?v=ix0Okt3XNQE