I use this to cover my MC-707 in the studio, and as a protective cover when travelling with the groove-box.
The plastic is of a sturdy kind, on that front there are no complaints, the plastic can even withstand a little pressure without bending out of shape.
When transporting, especially in vertical positions, the fit is not snug enough for it to hold to the gear through vacuum. For this I use a strip (or strips) of electrical tape along the edges, which makes the Decksaver less liable to pop off the instrument. Other people use things like belts or tape to keep them together.
Overall a great product, I try to get a decksaver with every sound module I buy, as it keeps your instruments looking pro and less liable to damage from dust.