Above is all correct.
I have had a Pertronix 1885 in my 350SL 4.5L djet for about 8 years. Never any problem. Only used to replace points so far.
The issue with leaving key in run position is true, but it is an unusual situation. If you do it knowingly, just disconnect the red lead. Changing to a Pertonix II apparently overcomes this problem, but then you need to make other changes such as suppressed plug wires which moves you further into non OE territory. Some have apparently done this, but not a great deal of experience recorded.
A Pertronix can just replace the points, or it can replace the points and the ignition module (MB call it switchgear). As a points replacement, it really doesn't do much more than eliminate need to set points gap/dwell. But it is more forgiving of distributor shaft wear/wobble.
The 1885 will work fine with copper core plug wires that are standard on our cars.
If you bypass the switchgear, you should also change the coil. But no need if switchgear is still working.
This link provides wiring diagrams (Ones that came with my Pertronix were generic and not much help)
http://www.benzworld.org/forums/r-c107-sl-slc-class/1714668-pertronix-install-without-switchgear.html
Definitely a good upgrade.