Rolleipol or Heliopan Kaesemann Polarizer

I can't help you with the performance of those two particular filters. I use Heliopan on the Pentax 67, both the top of the line multi coated polarizers as well as the cheaper single coated ones and I can't say there is any difference in picture quality whatsoever. I am not sure why you would want to get the very expensive Kaesemann version. I have used the unsealed Heliopans in the Sahara desert with no problems whatsoever. Be careful when using polarizers at high altitude as it will easily blacken the sky.
When I use the Yashica Mat I just hand hold a regular screw in polarizer in front of the lens since I don't have a bayonet polarizer for it. A bit inconvenient but works fine.

If you're worried about the color cast you should try your film of choice with the particular polarizer. Set varying strengths of polarizing effect and see how it performs and what the proper exposure compensation is. Here are a few examples:

Heliopan polarizer/Fuji Pro 400H

Heliopan polarizer/Fuji Provia 100F - shows the tendency to blacken the sky. Set the polarizing effect to a minimum or near minimum to avoid this and make sure you're not underexposing slide film slightly, as the polarizer will probably ruin the photo.

High altitude sky turns purple or black with a polarizer. You are better off not using one when there is sky in the image. It's still a good choice for shooting rocks and trees because you get better contrast.

Using a single polarizer with a TLR is a waste of time. Use properly, you have to observe and fine-tune the angle, which is impossible if you can't see through it in real time. The Rolleipol is a better, perhaps the only practical, choice.

Chrise, thank you for your input. Examples are most appreciated. Reason for me narrowing down to these two options is that Kaesemann and Rolleipol are both available in bayonet mount.
Edward: yeah that is something to think about. You are probably suggesting the polarizer which fits over the both viewing and taking lenses, but I think this type is not available in bay II (Minolta made one for the Autocord). Both Kaesemann and Rolleipol have scale markings on the rim to fine-tune and remember the angle when viewing through the polarizer, though it's a bit a waste of time, especially when used with the hood.

I have pol filters; early gas attacked me to "have it all" ...

I have used none of these in almost a decade and see/have seen no real need. I use Porta 400 UC or VC or Fuji 400H Pro to equally good results.

Andrew, there is useful info in this thread

Andrew,

The link that Chrise pointed you to is a good start to explain why you should be cautious with the older Rolleipol.
What that said, I have both of these filters that you mentioned along with the B+W Kaesemann version. I like the Heliopan, follow by the B+W filters followed by the Rolleipol. The Kaesemann filters, in my opinion are better because they are newer. From my use, I see a slight improvement over the Rolleipol. If you could find a Rolleipol that has not separated yet, then by all means use it.Consider this, you get what you pay for.
I like the number range scale that the Rolleipol & Heliopan has, in which the B+W doesn't. My Rolleipol has not separated YET, but I bought the Heliopan AFTER I bought the B+W version and found that I loved the number scale from which I view and then transfer it to the taking lens. Had I known about that, I would not had bought the B+W. Hope that this would help you decide which way to go. If Bob Salomon from HP Marketing is here, he will explain the difference form the Kaesemann polarizer filters over the non-Kaesemann filter of which the Rolliepol is.

Evan

Polarizing filters are constructed of a polarizing film (plastic) between two pieces of optical glass. Circular polarizers have a fourth layer, a 1/4-wavelength "plate" film next to the polarizing film on the camera side.

A Kaesemann filter takes the additional step of sealing the edges of the filter in order to exclude dirt and moisture. The Kaesemann company was acquired by B+W in 1989.

I have two B+W Kaesemann polarizers, screw thread and bayonet (B60), and neither has position markings on the rim. I've seen cheaper filters with reference marks (dots every 10 degrees or so), which are not numbered and of little use unless the filter is positioned and rotated exactly the same distance each time it is attached to the lens. The bayonet lugs on a Rolleiflex are offset 60 degrees between the taking and viewing lens.

To make a long story short, there are some tasks for which a TLR is not well suited.

Using a single polarizer with a TLR is most definitely not a waste of time - I used one for many years with a Mamiya C330F.
Sure, it's not not the easiest of cameras to use with this type of filter, but it's just a case of having to turn the filter in front of your eye, then note the position of the index mark on the filter rim (or make your own mark on the filter) before attaching it to the camera and adjusting the filter so that the rim is in the same position.