It is fine to book through one of the opaque vendors such as Orbitz or Expedia. That is, unless something goes wrong and you need it fixed. With the exception of day-of-travel IRROPS, you are stuck dealing with a vendor which only makes money on volume and loses money as soon as it has to have a live interaction with you.
FT is littered with the bad happenings from people who may even have saved a few dollars (or Euros) but wound up spending a lot more.
In particular, DL does not charge a phone booking fee, so there is no issue in speaking with a DL agent who, if they louse up the ticketing, can and will fix it.