Its the fastest way because almost 90% are underground , other 10% can be outside but just a little part of the vein , the rest its buried
And why its a bad mec ? Its like a metal detector dude , pretty easy to notice that faster ping the bone more close are you from silver
The slow way its use a staggbreaker and hit the ground , if it says "too hard" there is where u have to dig , usually are where golems spawns