They are very knowledgeable, professional people who know what they're doing when it comes to software development/testing (i have used them for many years).
Their support staffs also provide great follow up service after we've already signed off with our project manager that everything was going well during their QA phases - this reassures me because I'm always having second thoughts about my projects! No dislikes as of yet :D We run into issues occasionally where things need tweaking or adjustments but there's no issue at all being pushed back so long without resolution. When you work out your budget requirements before hand make sure its realistic since some clients will be demanding unrealistic prices which might result from poor communication beforehand between both parties involved :).