It's a must! I ordered one from aliexpress but never received no other place to get it!!
I think don't worth the money!!try this (although fairly expensive for what it is):
Keep your bike & your expensive riding gear clean with the GIVI mudflap mounting kit for BMW G310GS. Works with the RM rear mudflap to block dirt & debris.twistedthrottle.comReduce the amount of mud & debris flying off your rear tire with this GIVI RM02 rear mudguard. It'll keep your motorcycle looking fresh. Easy install.twistedthrottle.com