Those are great!
Here's a different design.
When assisting at a woodturning class at John C Campbell Folk School almost 15 years ago (Mike Stafford was teaching box-making), the native American flute-maker/instructor Billy Whitefox visited the woodturning area and asked me if I could make a small flute on the lathe. Sure, why not?! He provided the specs, I did the turning.
He uses a piece of bamboo or carved wood over the first hole which directs air over the second hole to make the note. I don't know if this is rightly called a "fipple" since it doesn't have the internal structure of what I understand is commonly referred to as a fipple, but it's function is to direct the air. It sure worked though. This is the way he made many of his flutes, some quite large.
I made a sketch before turning. Simple design, 2-finger-hole flute, open on both ends.
You can see the first hole is angled to better direct the incoming air across the hole that creates the sound.
The adjustable wood piece was shaped with a knife to better hold the tie ribbon, adjusted to get the best sound.
It was surprising how little air it needed.
After he saw my 'magic" wands, the next evening he asked if I could make what he called a "spirit whistle" in the handle of one. Sure, why not?!
It uses the same design to make the sound - he heated the bamboo in a flame, I think to shape it a little.
Since the cavity volume is small the pitch is high but it works fine! (I kept that one.)
It might be hard to see but I drilled several vent holes just after the two finger holes so the end wouldn't be closed.
The turning shop was popular that year. We had after-hours visitors most evenings, including a number of folk school staff.
JKJ