I have a page describing how I lay k-Track, including a section on how to cut it, at:
https://cabin-layout.mixmox.com/2005/07/laying-k-track.html

I use the Xuron 2175M which is specifically designed for Maerklin track. I have gone through 3 boxes of flex track where each piece needed cutting of at least one rail, usually both and this cutter is still as good as when I bought it.

Peter

Dremel with cut off disc No. 409

Beware that the 900mm flex tracks have one rail secured at each end. Therefore if you want a long sweeping curve you have to cut it off just after the rail tie, or it wont bend.

Well each to their own but you get 20 discs in the pack - more than enough for a large layout. Yes, they are fragile and can break but they do excellent thin cuts for isolation gaps and cut through rails effortlessly.

In my experience the disc diameter is more important as I have often needed to get as much reach as possible to achieve a vertical cut in situations where I haven't cut or been able to cut the rails before laying.