FT,
Well first of all I'd do the research. Check out that article for starters; sure it gives positive slants but it also tells you about the problems they've experienced in the past and how they've got over them.
The market in Cyprus is opening up and Helios are really the first airline to make a go of it since de-regulation. The only other charter airline is Eurocypria which is a sub of Cyprus Airways.
As with many Charters, the main concerns seem to be over winter but you'll notice they're now increasing their scheduled loads, so I think they're making all the right moves.
Moving job is *always* risky because there are always unknowns. However, none of us would get anywhere without taking risks. From what I know of Helios, they're no more risky an option then anyone else.
What do you do for a living? Have you been offered a job with them?