I have used them in the past & found that unless you are going on a complicated itinerary, the best thing to do is to book directly yourself.
I use the www.dublinairport.com location finder to see who flies directly to where & then www.tripadvisor.com to select a hotel I want to stay in.
Their surcharges for booking flights can be quite expensive and I have found that they can be slow in responding to queries.
Regarding travel with USIT , I used USIT www.usit.ie to get a J1 visa to the USA a good few years ago and I think http://www.sayit.ie were always much cheaper for everything including the visa I paid for and Sayit has a range of round the world and adventure trips also.
It might be worth your while checking out Sayit and comparing the deals.