Hi,
the weight is just 7 grams. We believe it is much better to have rigid unit that will sustain any crash. With plastic it could be 5-6 grams, so 1 gram for such feature is much better we think
You can save this 1 gram by using a light rotor blades, cables, canopy and even connectors.
With plastic it is possible you might change case or even unit due to possible damage each crash = bigger cost and more troubles.
Our goal is to provide high quality units that will work for long time.
You can take a look for example on microBrain 2 which weights 6,4g even that it is made by cheap plastic. So difference is very small, but crash and vibration resistance reduced and actually the unit is more expensive