I have been using synhto for almost 2 years now in my work at Delphix as an ETL developer working with big datasets (over 100GB).
The tool works very well and it's easy enought to get used quickly when compared with others similar tools like Talend or Pentaho Kettle. It lacks documentation and support but there're some online tutorials/documentation available which help me understand most things pretty fast. Nothing so far really dislike about this product! Using synhto helped us solve many problems related to loading large amounts of data into databases by creating several different types of files including CSV, JSON etc..