Hi Charles,
I am not sure about the multiple manufacturers... in my sizable collection only Studer uses them. Among the companies not using the butterflies are Ampex, MCI, Sony, Digitec, Tascam, Telefunken, Lyrec, Otari, Nagra and probably many others. Hardly a bunch of inexperienced players.
If you look at the four cases that I outlined, you mostly see a bit more noise here... a bit worse crosstalk there... so the question then becomes - why do it? I am not sure what you mean by the frequency response - I have not seen any effect of that pole shape.
As I stated in the video, there IS a minor positive effect when both recording and playing wide tracks - one extra dB of SNR... which might be noticeable in a studio. But the typical consumer case of playing narrow tracks with a wide head produces only the double-minus result.
When I compared the Otari and the Studer heads connected to the same tape preamp, it was an easy win for the Otari. Was the butterfly nature of the Studer head responsible for that? Perhaps... especially since in that test it was not able to get the additional help from the crosstalk compensation.