Hi, I'm new, and not an expert at anything. I have a M Audio profire 610 and a Saffire LE. At the time of my purchase M Audio, or Avid (digi design) products were required to run pro tools. Thats not the case anymore with pro tools 9. As a piece of gear they are very similar in performance. I suggest to compare features to see what is best for you, for example, the M Audio has 2 firewire ports, the Saffire pro 1. and the bundled software is a bit different in each, personal preference is the decider.
There is usually a limit to the number of times you can connect to different computers.
My Saffire LE is 4 I think the 610 is 1, check with the M Audio site or your local retailer, some salesmen are clueless, most however, are not, get a second opinion. The Saffire pro is $150 cheaper than the M Audio. I am happy with the 610 and it is the one I use all the time. I have no experience with
the FireStudio Mobile, Hope this helps. By the way this is a great site and the advice I have received has saved me a lot of headache, and money.