I had mixed results using RedSDK in 2018 and 2017.
The first test, the first was a 25Mb file with lots of materials, it did not crash, but every object which had a material applied in 2018, vanished, so saving the file in 2017 went from 25Mb down to 258k.
The second test (a simple cylinder added to a cube), if an object has part tree information, it survives the process, but if it is just listed as an ACIS solid, it vanishes, though those which survives, in 2017 it locks the object as far as materials go, so I cannot add materials, at least until I explode the part tree back to an ACIS solid, then I can add materials.
Not good really. as a side note - saving as a .sat (ACIS) file, allows all the objects to survive, it just wipes off the materials.