You're not just buying a camera. You will be investing into a system.
Lens, flash are only Sigma SA-Mount. As good as a camera it may be, it might not be the wisest choice to buy into. I used to be a Sigma mount user - The SA300N film SLR. Good camera, too small user base, hard to buy/sell lenses and accessories.
Of course, there are some who aren't bothered by this because they know they aren't going to buy/sell/trade with anyone else. If this be the case, and you're satisfied with its performance and what it could do for you, then go for it.