@tomg what I've read some people seem to dislike varistors just because the can fail causing a short. If you don't have a fuse before you will have a fire. Have a look on Wikipedia under hazards.
Offcourse with a fuse this seems to be a good tool to avoid surge damage with a MOV but I guess selecting it's values are crusial.
I'm don't have knowledge enough and it's been pointed out to me that selecting the varistor values and specs are very important. Unfortunately I haven't got that far in my readings yet...
Edit: myself are also using the HLK with MOV. Even one outside (under roof) and it's been working great for a while... so offcourse there might be a chance it was just an unlucky event.