Hi HP,
Interesting stuff, but we are in a diffrent world now compared to that of the service pilots in WW II. We have more experience than the students and the benifit of more corporate knowledge than the instructors. Our remit is also different, as is the way we fly.
Given the lack of flap on the engine off glide, I still believe the sideslip is useful. I also believe it's safe if it's first practiced at height to gain the skill.
VBW
A