Is primary open angle glaucoma progressive? Is it curable?

Yes and no. Primary open angle glaucoma is controllable not curable. Usually can be controlled with drops. With good pressure control, progression is also controlled. Occasionally laser or surgery is necessary.
Treatable. Glaucoma can progress, and untreated will lead to first peripheral vision loss and then central vision loss. It is treatable, and anyone with it should see an ophthalmologist for management. Vision loss can be prevented by treatment.