Regarding the few posts above:

1) Sometimes trip.com does not list parther FFP in the drop-down list, in which case its possible to ask them to do input it manually.
2) Its very important to set the region correctly in trip.com, the fares can differ significantly depending on the region and there may be some local offers.
3) Never had a problem with their English, although on my last enquiry, it was answered by a Korean agent with auto translate. Was not a problem
4) Generally agree regarding the LCC, in my case I often book very last minute and certain that there will be no changes/extra purchases to be made and trip.com lets you pay with local currencies without any markups, which is convenient.