I'm hesitant to post in this thread, not merely because I'm more intrigued by the doctrinal side of it, but also because I was somewhat taken back by the differences of experience with it in TWI.
In brief, about all I knew about SIT prior to TWI is what I read of it in the Bible and that some people did it, that all should be able to, and that I wanted to. (I had never actually heard it.)
About all it took was hearing two people in a believer's meeting (and seeing that each had their own unique tongue) to later that day lock myself in a closet (so to speak), pray to God for "the real deal" (in so many words), and then do it. What I did (and heard myself doing) then hasn't changed much in over 40 years. And to be honest about it, I don't believe that anything TWI (or anyone else) could, would or did do after that would ever persuade me any more (or any less) that it is not "the real deal." Because "that deal" always was, and still is, between me and God. And I don't believe He is an Indian giver.
So I don't know, and can't say what others experienced. Other than, it looks like it may have different. (But I don't know.)