There is always a risk in moving to another company, but Narrow Runway is making a calculated decision that seems likely to work out. From easyJet's perspective he is exactly who they want to apply, as he can be a captain easily within a year. As others have said, there are no guarantees, because if Stelios gets his way the expansion will be curtailed significantly. Also there is some economic uncertainty - that has always been the case. A factor to consider in that is that easyJet may do well from an economic blip as other less fortunate carriers go under. EasyJet have had a fantastic summer and look set to return a healthy profit for the year ending Sep 30th (results to be announced early November).
If a whole pile of highly-qualified and capable ME-based Airbus-rated Captains/FOs apply for easyJet, and I think that is quite likely, then easyJet will see this as a vindication of their recruitment policy of the last few years. Loads of instantly-promotable FOs in place who were all paid for by someone else, all with at least a year of easyJet experience behind them - hard to argue that such a situation is anything other than win-win for company and pilots alike.