Blades    Arms
With no sideways pressure the tip should point directly at the glass:

But when wiping across to the left the tip should lean right over and lie flat on the glass, which sweeps almost all the water away leaving just a microscopic lubricating layer that dries instantly:

Ditto on the return. If the tip is not pointing directly at the glass when there is no sideways pressure then one sweep will lean less than the other, and may judder:

The refills should be able to slide back and fore in the pivoting carriers on the arm so they can curve to fit any screen:

Vee's when parked touch the glass for the whole length except for the very end (arrowed):

And in the centre of their sweep lie flat and straight against the glass:

The arms should have some method of retaining them on the spindles. Mine have a spring-clip that hooks under the base of the splined section, and the blade has to be lifted off the glass to remove the tension between arm and spindle before I can remove them. If the splines are worn it may allow the arm to fly off when in use: