@2BagsFull,
Thank you for bringing this topic into the limelight.
Let me answer to your question b).
The supplier published pre-inflated diameters only, not post-inflated. Those are as follows for each model: SE 30 mm, ME 35 mm, LE 40 mm and LLE 45 mm.
However, actual measured my LLE is 50mm and the diameter grows to 80 mm after the air pump was pushed six times.
As for its quality, you need to be careful about air leaks.
One is at the base of the air delivery hose. Leakage can occur between the nozzle air inlet and the hose, but this can be prevented by tightening the hose firmly with a cable tie.
The second is the air pump itself. This can be prevented by replacing the pump itself with a good one, or by pinching the hose with a pinchcock after inflation to prevent air from returning to the pump area.
I have had to replace them for various reasons, but they seem to last more than 10 years if used carefully like my latest (actually, self modified for e-stim) one.