They're not actually trying to build a high-powered computing cluster, just demonstrate how one works.

They could / should switch to a Pi Zero or Zero W then, save more than half on the expense of the devices.

Or make it so you can plug in any Pi, is there anything of a secondhand market for those yet? I can imagine there isn't though, those things are cheap enough to be throwaway / lose in a drawer devices.

Neither of them is really high-powered, believe me. :)

But using one with old B boards could be excruciatingly slow at times, which is why I just had to upgrade mine - it’s since become a lot more productive in the sense that my tests take around 5 minutes instead of a whole hour :)

I doubt you're the only one on here with the understanding that a bunch of Pi's is not really a supercomputer cluster, but thanks for the clarification smileyface.

looks like the last update to the site was in mid 2015, so nowadays one should probably get the pi3 instead. However the github repo for the simulations is still empty.