Yes, it's awesome lens. Very very light, makes a nice alternative to monster zoom. But it's slow. IMHO it's just fine as I have never yet hit the ISO limit (12800 for my taste).
Sharpness is up there, nearly prime like. I have yet to test the corners exhaustively, but for general use, it's perfectly sharp closed one stop down.
I love the comptactness, the 49mm filter thread shared with the F 80-200 (which is ever more awesome that this F 35-80).
Overall, I'd say that if I only want to bring two AF zooms I would choose FA 28-70 AL and F 80-200, but if I bring my FA 20-35mm along, then the F 35-80 replace the FA 28-70 AL!
---------- Post added 05-15-16 at 09:10 AM ----------
Here are some takumars mounted on K1.
SMC Takumar 24mm f3.5
SMC Takumar 35mm F3.5 (with super takumar 35mm f3.5 hood)
SMC Takumar 35mm F3.5 (with super takumar 35mm f3.5 hood)
SMC Takumar 35mm F3.5 (with correct square 35mm f3.5/f2.0 hood)
SMC Takumar 135mm f2.5 6 elements version II
SMC Takumar 135mm f2.5 6 elements version II
SMC Takumar 35mm f2.0 with correct hood
SMC Takumar 35mm f2.0 with correct hood
Super Takumar 28mm f3.5 with correct hood
SMC Takumar 50mm f4 macro
SMC Takumar 50mm f4 macro
SMC Takumar 100mm f4 macro
SMC Takumar 100mm f4 macro