Hi,
that's good news. Excepting the rotor there are no moving parts in a stepper, it ought to be possible to make such simple devices without
fault. Roger was quite right to smell rat.
The only real quality issue I can think of that would separate good from not so good is insulation resistance, and not just the normal static tests
but the ability to withstand high voltages at elevated temperature working conditions for years at a time.
I bought Vexta 5 phase steppers for my mill and paid a real high premium for them. I wondered after I had committed to buy whether it was justified.
I also use Vexta drivers, they are 230V input with a switch mode supply to the driver. The DC link voltage is 150V. This is the highest voltage
I've ever heard of for a stepper motor. Whether the premium I paid is justified I'm glad that Vexta quality is such that their motors withstand those
voltages under working conditions and have done for four years.
Craig