I bought my TIG from Airgas on mass ave near South Bay. The guys there are Mike and Kevin. They're both really nice guys, which is awesome, esp when you're new. The attitude thing from Tolman is bogus, though they do sell balloons and magic tricks, and are open on sat.
There's an Airgas (both were formerly Linde until about a year ago) in Cambridge on Vassar, and the guy who works there (Milton) is as nice as dudes come, except for price.
I'd recommend building a relationship with the Dorchester Airgas. I think I'm going to stop going to Cambridge one even though it's waay closer for me (timewise, no cylinders through the big dig tunnels). You're going to have to buy shielding gas locally, so having guys like you is key. Shipping might be equal to tax. I'd bet on a tax free holiday in august, though if you can wait.
The Diversion looks like a nice machine. If you plan on doing Al, also plan on buying a liquid cooled torch, and maybe a chiller. I have had two torches ruined from (other people) inadequate cooling.