We used Edreams t all of the time to book flights to Germany until we booked one for out friend to fly to the UK. When she came to return home there was no return flight booked, just a one way ticket into the UK, even though the booking confirmation from edreams stated a return flight. She had to spend 290 euros for a flight to Germany (the original return flight was 50 euros).
After contacting edreams about this in April they said it would follow their standard complaints procedure and should take 30 days. After 45 days we emailed them asking for an outcome and they replied with 'it is taking our standard complaints procedure'. Not very helpful. Now another 30 days later we have still not heard a thing, despite 10 or more emails asking for updates.
They seem to be great at getting cheap deals (although I now wouldn't trust them to book them correctly) but should you have an issue you will find them unbelievably hard to get a hold of.
In short, yes they are cheap, and probably most of the time they are competent. Just beware of customer service. Very lacking.