I used to use the more well known ones like Opodo and never had any problems. I was doing a search the other day for a Biz class return fare from EZE to the UK which returned some very cheap results. However the outbound trip was via Bogota with Avianca then onward with Lufty via Frankfurt. The total travel time was close to 36 hours so I soon dismissed that one. Especially as I'd never heard of the OTA before. I'd far rather cough up the extra to fly more direct.