Aye ive heard those jigsaw blades are OK on 50mm pir but not very good with 100mm PIRFor cutting PIR I used a jigsaw with a bradknife serrated type blade. Made a nice tidy job of it without hardly any tearing or dust from it.
To get PIR to fit nicely, you can use Gapotape. You only have to get the cuts sort of accurate, then the memory foam compresses. Also improves the vapour barrier. It is however and additional cost and takes more time...