I checked out the spec sheet. Thermally, it's pretty standard for XPS (k-value), but polyiso board is definitely a better insulator (but more expensive). If your tight on budget and don't want to upgrade to polyiso, I'd say go for. One thing does jump out though: the fire rating is E, which is pretty much as low as it get. It means the product is combustible, with no flame-retardant performance. Something to consider when wiring - make sure you size your wires well, install the right fuses, and make good electrical connections!

I think you forgot to attach the image / link Boycee! However from my research just now, Fastwarm is XPS or EPS rather than Polyiso. Broadly speaking Polyiso is a better insulator (and a lot better for the environment). However there's not much in it. It's worth looking at the spec sheet for the insulation you are looking at to get the R-value (Discussed here: https://www.thevanconversion.com/post/van-insulation) How many cm's you looking at getting and what sort of temperatures / seasons / geographical locations will you be travelling with the van?

Great to hear you're back on track with your build after everything that has happened! Don't be shy about reaching out if you ever need help :)