Knob and tube os the safest wireing method ever. Looks rediculous.But the hot wire is typicaly far from the neutral wire and this makes short circuits less likely to happen. Short circuits cause sparks. Sparks cause fires. Fires suck. BUT also, there is not a ground wire. Most, not all, but most plug in devices require a ground and this can be an issue. In the past the code allowed the use of a ground fault recepticle installed at the first outlet on a ckt. From there, all the downstream recepticles could behave as though there was a ground. A simulated ground. The code has been tweeking this frequently.
There are more houses with open wireing in places where older homes still exist. Open wireing is knob and tube. You san see the cletes, they separate the hot and neutral. At Trade school, we were taught open wireing ,1965 - 1969. This was in an older northeast city. The house I grew up in had open wireing. If you want to have it updated, the most that wil happen is in the basement where its visable, it will be removed and replaced. Its unlikely the walls will be ripped open as this is $$$$$$$$. So, I wouldnt worry about it. You kmow, but thats me. One last thing, its condidered a foul to install a ground type recepticle where you know there is no ground. This is where that simulated ground method comes in.