The majority of contractors are happy with the deal and what is permanent these days? my understanding is that the plan is that NAS will establish companies in the countries that they operate and you will become an employee of that company, the company is growing very quickly and have an ongoing need for pilots for the foreseeable future, the money is excellent and the company culture is the polar opposite of Ryanair, they will genuinely do what they can to accommodate you, but they have a business to run, you will not be based in Norway,Sweden or Denmark so don't worry about core.
Basing is fluid due to the nature of the Nordic winter market, so a lot of people will get moved to LPA/TFS over the winter, but as the business expands this will become less of a problem.