Pros
I've been using these guys for the past year and a half and they have had some great results with me. I oversee UI and RoR teams and have been overseeing similar teams for the past 5 years. Until working with Fortitude it had been very hard to grow each team, aka find great developers. These guys seems to find the niche developers quickly. I've hired on 2 developers for each team since we agreed to do business and all 4 developers have done great work so far.
Cons
Not many, they do move fast so as a hiring manager you have to be prepared to move fast as well. In the software world I'd rather have my recruiting firm have a fire behind them. They have missed a couple times but it hasn't been often based on the amount of times I've worked with them.