FWIW
I just received a set of YZ490J DC plastics from Les at VMX. When i called him, he asked which brand I wanted and I told him i wasn't worried about price, just wanted the better plastics.
His advice was that the Maier was sort of shiny but didn't fit properly and that the DC would fit but wasn't shiny... but he recomended the DC......
A mate just recieved some 490 Maier sidecovers and I had a look at them side by side along with the original plastics & DC's, In my opinion the DC aren't great but the Maier just aren't right. You can see the DC are made from molds off the originals but it looks like Maier have made there own molds from scratch because they are not the right shape or profile and small things like the recess for th 490 sticker on the sidecovers are missing all together.
I know there may be some variations in quality from model to model in both brands but I recently also bought a maier rear guard from the US (VMX Racing -be aware, very dodgy) for a CR250, it was so bad I tried to return it, when they wouldn't return it , it went straight in the bin