This set come with three designs, two of each, and retails for £6.50. You get these three designs in the set:
Wooden top with fungus.
The designs are on the organic side of things, and would suit "new" chaos' more organic shapes. Each backpack has a hole in the back, allowing for easy fitting on other marine models. The backs are detailed though, so you might need to file them flat if you feel there isn't enough surface area for the glue.
Worryingly, the organic nature means it's harder to remove the thick resin sprues and mould lines without damaging the pieces. Careful knife-skills, plus some green-stuff for afterwards, if your best bet of removing them.
Once removed they do look good on model, and as expected, they fit well with other Spellcrow components.
All-in-all, they are a nice addition to Plague Legion/Marine armies, that require a little more care when it comes to de-spruing mould-line removal.