These pumps are well made and from what I have seen, run very well.
However, all pumps using this type of valving on the steam end do NOT like getting shot water instead of steam.
If you should accidentally fill the steam end with water, you pretty much have to take off a hatch and blow the water out - you cannot just keep up the pressure and expect the water to be expelled...won't happen.
As long as you are careful about startup, you should be very happy.
Living proof that just about anybody can build a working loco...