One of Europe's biggest low-cost airlines is selling a year of unlimited flights for $550 — but it comes with a whole heap of strings attached

• Wizz Air is offering customers unlimited flights for a year for 499 euros ($550).
• The unlimited pass comes with big caveats, namely that you can only book flights three days ahead.

Wizz Air, one of Europe's largest ultra-low-cost carriers, is offering people the chance to buy a year of unlimited flights for 499 euros ($550).

The Budapest-based airline launched its "All You Can Fly" membership with an introductory offer that means it is 100 euros ($110) cheaper than usual until Friday.

It comes after Wizz was named in June as the worst airline for UK flight delays for the third year in a row, according to an analysis by the PA news agency. The firm's stock is also down 34% over the past six months.

However, there are several caveats to the unlimited-flight pass.

In small print, Wizz notes there's a flat fee of 9.99 euros ($11) to be paid separately for each flight segment.

Passengers would also have to pay extra for any luggage beyond the basic allowance of a personal item. Plus, tickets are only available within 72 hours of the flight and are subject to availability.

Wizz seemingly acknowledges that the last point means pass holders could struggle to book a return flight, referring to this in the FAQ section. It notes that pass holders could instead "book a flight using the regular booking process."

With 924 routes as of its last annual report published in May, Wizz offers an extensive network. That includes routes to the likes of Dubai and Uzbekistan, which aren't available on budget competitors Ryanair and easyJet.

A one-way flight between London and Budapest in three days' time starts at around 81 euros ($90). So including the extra flat fee per flight segment, you'd only need seven of these to break even. However, a one-way flight on this route is as low as 29 euros ($32) if you book months in advance, meaning you'd only break even after 27 trips.

The deal may well appeal to frequent flyers — a customer category that's typically disregarded by budget airlines — but its appeal is less clear for regular travelers.