Isolating a section of already-ballasted track?

[faraway]

Just make sure you get the right ones .....these cut differently than the ones in Reinhard's pics .....

Nope, mine has the same function. It is just another brand. The one you show is also available in Germany. It is sold with the very true disclaimer to use it for rails only. But it is sold at moderate price. I got sick of it after I ruined three of them and bought a flush cutter at a higher price (about $60) that sustains wires used for my switch machines too.
The little reds are dangerous beasts. You can get very much used to a flush cutter to cut a lot of things....and kill the red ones soon.