Bredok3D claims that they are in a partnership with Microsoft (I guess it’s true since they are featured in the Marketplace) which means they are free to use Asobo assets in their products (another example is Carenado using the Asobo G1000).
Regarding its quality, Jörg made it clear in an older Q&A session that they do not plan to curate the Marketplace, it is up to the users to do so by utilising the voting system (though I agree with many others that written reviews would help a lot in that regard).