Mine came with a extra spring, so I installed.
After putting in a fresh battery I could get maybe 2 or 3 activations. Then the unit would not fire, Check battery level....1.2v or similar.
Check battery with multimeter 4.2v. Then no matter what battery you installed it would read low voltage.
Give it a hour or so with no battery and you could put in a battery and get a couple puffs.
If you checked resistance with Vamo it would read correctly, then the next activation or maybe 2 the unit would show atty as being too low.
Same thing...give it some time with no battery, and it would act normal for a minute.
I think I just got the dud.
The vendor had me send it back, (now I just hope it will act up for them.)
There is always going to be some small failure rate with equipment, so it is no reflection on the vendor.