They do something very pernicious when displaying the price of extra options for return flights.
Instead of showing you the total price for the return flight, they show you the price of the option on the cheapest leg of the flight. So for example, if an option cost $10 on the outbound flight, $15 inbound flight, instead of displaying $25 total or $12.5 on average, they display "From $10 per flight". You'd expect to pay $20 but end up paying $25.
Legacy airlines do this too. “Upgrade to business class from $100!” Turns out it’s $100 for your random short connecting flight, and $2000 for your main flight.
Instead of showing you the total price for the return flight, they show you the price of the option on the cheapest leg of the flight. So for example, if an option cost $10 on the outbound flight, $15 inbound flight, instead of displaying $25 total or $12.5 on average, they display "From $10 per flight". You'd expect to pay $20 but end up paying $25.