Used them on a Gatwick to JFK recently. Was supposed to be the Dreamliner both legs.
Outbound to JFK was almost 5 hours delayed. They rocked up in a clapped out A340. Business class was a disaster. They used HiFly to infill. Christ!
Inbound from JFK they again used HiFly. This time they rocked up with A330. That went tech due to avionics gremlins in flight deck. They cancelled the flight.
No direct Gatwick inbound seats available with them for 2 days. Only way back to Gatwick on sane departure date was fly to Oslo then backtrack to Gatwick.
On the upside the JFK to Oslo was Norwegian and on a Dreamliner. Transferred to B737 Oslo to Gatwick.
Norwegian need to dump HiFly. Totally sh1t setup. Aircraft were dated and nothing really worked in business class. Toilets were disgusting. In flight was poor.
Based on that 1st time experience I won't use Norwegian again. Neither will the other 4 business colleagues in my company. Complete amateur's trying to run transatlantic services. Never again. Steer clear of them. Use Virgin or BA.