Yes the rhizisomes are the edible part, but they are very difficult to grind, so that is why it’s generally sold already ground up. Getting it from an Indian Market would likely be the best way of getting fresh I guess.
Many studies have been done that show good results for helping with many issues. Those studies used supplements - not the spice itself. The main ingredient that helps appears to be the curcumin.
Tumeric turns every thing yellow. It’s one of the ingredients in Mustard too IIRC. I have thought about getting capsules, and making my own supplements from spices, but haven’t seriously pursued that - more like a passing thought.LOL
Many rhizomes are edible, although quite fiberous, and can be easily ground with a micro-plane while still frozen.
A micro-plane is actually a woodworkers tool, that is re-purposed for the kitchen, similar to a rasp or a file.
The micro-plane allows the removed material to fall though the tool holes to be collected,
whereas a rasp, or file will trap the material on the tool teeth, and requires separate action for material removal/cleaning.
I imagine a micro-plane could be used on all rhizomes and fiberous root crops such as tumeric, yucca, ginger, carrot, sweet potato, etc., etc..
A worthy investment !