I have been working with them for over 5 years now - we are currently doing two projects together at once (one internal to their agency).
They always deliver high quality work which has allowed us as clients be very confident about delivering our own project outcomes! Sometimes it can take time getting used too but they're quick responses mean things move along quickly enough that you don't mind so much :) As said above though there's not really anything negative i'd say either way; just keep going back if your needs change or evolve throughout development of new/existing products / services etc..