Would I use the BM257 to probe the wall sockets at 240V? Sure. Would I use it in the distribution panel? I think so. Would I use it on industrial electrical equipment, power feeds from the grid, or in power stations, no.....
For anything almost any hobbyist would think of using a mulitmeter for, I think the BM257 is a very good and safe meter.
As chainsaw said, you cannot measure the impedance of cables with a multimeter. Watch ths video by one of the forum members on how to do so.