I have had one or three Zinc oxide MOV units, NOS GE ones, in the red dipped package, die short circuit while in storage, but in general with 230VAC mains they will all ineviatably fail as short, so best is to make sure they are fused correctly. But as all of those I have used failed safely, small one blowing apart, bigger ones drawing enough current to trip a breaker rather rapidly, often with no apparent damage to the MOV, other than it having a low varying DC resistance, in the order of 10's of ohms, with 1V applied from a multimeter, as opposed to being well over 10M normally. Seen also units with fuses in the path to the MOV units, either as PC board traces, or a proper ceramic fuse soldered into the board, or for the one, with a 20A ATO automotive fuse soldered into a slot in the board. Last one made by Clearline, guess they were happy using a 20A 32VDC rated fuse well past the warranted ratings.
I have plenty in use, often simply mounted in a connection block to an external LED light, to keep the surges down, to keep the lamp life as long as possible, even if the lights are rated for 3kV surge, extra always helps. they still all fail after a while, some soon, some after a year or two, and a few that still work after 4 years.