I was thinking about giving soda blasting a try with a view to using it to strip paint of ancient GRP (so soda for starters and maybe something a bit more aggressive if needed)

so I was keeping my eyes open for a air gun etc. to make a DIY setup, but then I spotted this kit:
http://www.frost.co.uk/automotive-new-products/abrasive-n-soda-blast-intro-kit.html

any thoughts ?

Use normal baking soda from the shop; it's cheaper.

It's also non-toxic and can be washed away with a hose.

Ive got one of those cylinders that you fill and attach to an air line. Really good kit, but works the compressor hard. I never really got on with the soda (makes a right mess, and is impossible without an air fed blasting helmet), so went back to iron oxide which works as well, and also etches the surface for powdercoating.

I thought you meant this one linky
Strikes me someone could have been killed!
Look at the size of the fricking holes.
Cheers, Pewe10