I booked tons of tickets over the years using ITA as a basis.
Its not that difficult. Get the itinerary finalised in ITA and then either:
(a) Head over to the appropriate airline's website and enter in the legs; or (b) Call up the appropriate airline's reservations callcentre
The savings achievable via ITA far outweighed the minor inconvenience of double-keying.
I booked tons of tickets over the years using ITA as a basis.
Its not that difficult. Get the itinerary finalised in ITA and then either:
In 99.99% of cases, I was able to do it all online without speaking to anyone. There was only a tiny number where I had to call them up.The savings achievable via ITA far outweighed the minor inconvenience of double-keying.