I have had this done at Jiffy Lube about 4 years ago and never had any ill effects to my trans (over 200k). I would do it every once in a while because the trans fliud was really clean after it was done. The thing I didn't like was the filter was not changed during this procedure nor was the pan removed. Your trans cooler gets flushed thoroughly along with the trans lines and such which is good. I believe it is safe.

__________________
1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T