This is a great thread. As far as I know, and by what I have experienced or heard from others. Such as clients that have received both. Myofascial release does not hurt, at least I don't think so. (John Barnes style)
Acupressure, or Trigger point is only supposed to be "mildly uncomfortable" while holding the point and waiting for release. When I practice TrP Therapy (which I have studied endlessly), I use verbal cues. Such as when I am gently slowly applying pressure, to the TrP, I say"tell me when discomfort is a 7 out of 10" Because this varies for everyone, the verbal cues are helpful. Then I hold and ask to tell me when it goes down to a 3, because it will. Then back to 7, back to 3, without ever letting up completely. But, never "pain" and I never use that term for verbal cues, too negative.
I have had a client that went through a 10 session Rolfing Structural Integration series, by a Rolfer that actually studied directly under Ida Rolfe. And he said, and I quote "it hurt like hell, every session".
However, I am not an expert in either style. So it's just hearsay and personal experiences. I did once have a therapist that worked for me that was crazy deep. She practiced under the old school means of therapists years ago "NO PAIN, NO GAIN", which is absolute hogwash. She told people her technique was "based on Rolfing, and Hellerwork" But never took a course in either, let alone being certified.
There are definitely people out there that claim to be MFR therapist, that are doing it wrong (in a traditional sense, because they never were certified), and have made up their own style but call it MFR. Who is to say, who is right and wrong. I personally wouldn't lay claim to a style unless I was certified, or I developed a style and gave it my own name. Such as Tom's Anatomy Trains. He invented it, it's his. If he says it's supposed to hurt, it's supposed to hurt.
I don't even know...is MFR even a trademarked name, because it is almost as common as saying Deep Tissue nowadays.