I bought three 731B all shipped to here in China with no problem.
One good thing about 731B is that is consumes very little power from the mains. The current of one of them from the 220VAC mains is only 2.3mA, which is 0.51VA(not Watt, VA is the apparent power, the real power is even smaller).
One bad thing about the 731B is the very poor implementation of the transformer: no insulation between the primary winding and the shield winding.
The shield winding was shorted to the primary winding one day in one of mine, making the power cut for the whole house because of the leakage protection. I teardown the transformer and found out that there is NO insulation between the primary and the shield made of bare copper sheet.
Edit: add photos
The green/yellow wire is the shield, which connected to the earth(and connected to the case/chassis/metal power switch as well).
Red, orange, brown and black wires are the two primary windings. The copper shield is directly wrapped around the primary winding.