Omega Flight Store are legitimate, although a bit patchy in terms of customer service if Trip Advisor is to be believed. I had a recent experience where I booked through Skyscanner and then ended with a slightly dodgy booking site, but payment through PayPal’s credit card portal. After I paid I got a booking confirmation and then an email from the travel agent in broken English asking for pictures of my passport and both sides of my credit card. Needless to say, I declined. However, I did phone the airline (Hainan in that case) and the booking was fine and all went smoothly. The price was 50% of the cheapest price I could get on the Hainan web site, but I did keep my doubts from my wife and was prepared to just buy expensive tickets at the airport if I had to.