Zonda - the whole can of worms right there ! There are those who say only the M visa permits flight training. There are those who say that the visa status is mostly irrelevant to the training if less than 18hrs a week. You appear to occupy the pragmatic middle ground ( as do I) except that where is the difference between ESTA and a B1 visa? . And how does one determine factually if you can train on a particular visa - no definitive answer to that exists, no guidelines about what actually constitues training eg everything from an hour dual through a 5 hours float rating up to to a PPL or CPL course is training.! TSA will give you training approval as long as either a. you are out of the country or b. you can prove you are legally in the country ( entry stamp, any method including esta).