I just went through the same decision as the OP and ended up with the Kowa paired with a 500AH. I just don't see myself using the modular system of the Swaro and I hate chromatic aberration which the Kowa handles beautifully. The fact that I could buy the scope plus the 1.6x extender, plus case and tripod head and still come out less than the Swaro didn't hurt either! The 883/500AH is an almost perfect combo. The 500AH is a big head in volume, but doesn't way a ton and the pre-set drag is just about perfect. It was very easy to balance the scope using the spring balance and supplied manfrotto plate. On a recent day on the water, looking west into the sun (birds were backlit) there was zero and I mean zero purple or green fringing--just incredible!
My only complaints (and they're minor) is that it is not compatible with Arca-Swiss plates...I have lots of Kirk plates and none of them work. Second, the lack of rubbe armor is noticeable--the scope feels delicate and would certainly take on damage from even a small drop onto a hard surface. A Kowa canvas or neoprene case is a must (I have the canvas which is functional, albeit ugly).