I bought a used Dumore hand grinder a few years back, and I ended up throwing it out. Turned out there were breaks in the winding, and they could not be fixed. I don't blame Dumore, because I don't know what caused the breaks. It was supposedly NOS when I got it, but maybe someone abused it and ruined it in a hurry. Of course, an industrial tool should stand abuse well, so I don't know if Dumore has an excuse.
While I had it open, I noticed it was a piece of junk. The bearings were cheap and small, for one thing. It was worse than a Dremel. I was amazed. I thought Dumore was a quality brand.
I have a Makita which cost way, way less than a Dumore. I paid $124. It has much bigger bearings and is built much better. No comparison. It's far superior in every way. I found out Makita was once known for balancing motors, so I guess they know what they're doing.
I'm pretty skeptical about Dumore because of this.
I don't think there is a practical way to add a flex shaft to the Makita.