tl;dr: They didn't actually book the tickets I booked with them and didn't notify me so I missed the flight because of them.
I booked a flight with them and when I wanted to check in following their email asking me to I couldn't. I contacted their support and was told that I had no tickets because the booking failed. This was on the day of the flight! They didn't bother notifying me at all about this but continued to send emails asking me to check in. They just said I have no tickets and made zero effort to help.
I've seen a lot of bad airlines and a lot of bad OTAs but I've never seen one as incompetent as Opodo to not actually book the tickets. This is the last time I use this joke of a company.