I used to have a Takumar Bayonet 135 as part of my small collection of 135's from back in Ye Olde Film Days of Yore --
[A* 135/1.8, VS1 135/2.3, K 135/2.5, Takumar Bayonet 135/"2.5", K 135/3.5]
I found that the Takumar Bayonet 135 was a decent enough lens for build quality, resolution, and contrast, just as long as it didn't have to deal with any bright lights -- IMHO, its only serious drawback was its susceptibility to flare, either obvious geometrical flare markings or overall veiling flare. SMC does (at least sometimes) make a difference --
[K 135/2.5, Takumar Bayonet 135/"2.5"]
However, the lens must have had its "135/2.5" specs "determined" in the marketing department, since it really is a nominal 135/2.8 lens. 135mm / 2.5 = 54mm, while 135mm / 2.8 = 48mm. And the Takumar Bayonet 135's 52mm filter threads (unlike the K 135/2.5's, which measure 58mm) allow for probably only 49mm or 50mm (at the most) of clear front aperture. [Of course, this is not unlike the K200/"2.5" which, with its 77mm filter threads, is probably actually a 200/2.8 lens.]