I have Mavic UST rims (open pro). UST is Mavic's attempt to get a standard fitting for tubeless tires so they all fit on easily and safely as there is currently no industry standard as to guarantee one brand's tire will fit on another brand's rim although they usually do. So if you fit UST tires you will find them easy(er) to mount and they should not be in any danger or coming off.
However it seems the initiative has been a bust as no other manufacturers have adopted the standard. That said, there's no downside to it as you can still fit non UST tubeless tires if you want or even tubes (I run tubes).