I prefer purchasing things through Steam since I get to pay in local CDN, and throughout the year I'll sometimes get Steam credit as gifts

I bought the heavy performance pack on Day 2, since i had extra funds in my Steam wallet and 20% off seemed like a fair deal. I also really liked the design of the Thunderbolt and getting the iconic Mad Cat was a great bonus too. I've since bought two other variants of the T-Bolt with cbills and have maxed out basic skills on all three.
Eventually, I'd like to experiment with other weight classes and it would be great if Mastery packs were available on Steam!