It'll be half price between the 21-28th December, so grab it then.. :)
Truth be told, the PC-21/PC-9 and T-6B are similar insofar as they're all Turboprop trainers.
The PC-21 is against the T-6B in a number of markets so they're similar in content, though the AT-6 features COIN capabilities but we're not planning that until next year.
The PC-9 whilst a fantastic simulation, is an older aircraft than the T-6B. I often think the PC-21 is a Ferrari, whereas the T-6B is your all American muscle car :)
Personally, the T-6B has a lot going for it if you're from a country who is likely to use it (US, UK etc) whereas the PC-21 is the same but for the European market. Each to their own really, both products have our heart and soul poured into them.. :) Just up to you on what...