I've wondered about using this for a while but never seen any other articles on using it so I thought I'd see if it works..
So I found a few pieces of dead elder (sambucus nigra) and took the pith out of the center
put it in the usual char tin and in the fire just for a few seconds as it chars incredibly quickly
then into the tinder box, I broke some of the pieces up to increase the surface area and create a better chance of getting a successful spark though this may ultimately not have been a good idea, the steel was struck with a piece of flint onto the charred pith
and as you can see it took very easily.. However there are a few downsides, if you put the tinder bundle into your tinder box to blow to flame the charred pith blows out everywhere as it is so incredibly light, the slightest movement of air scatters all the pieces so be gentle.
Also putting the embers into a 'birdsnest' tinder bundle and blowing it to flame is tricky, it's hard to keep all the little pieces together so the ember spreads as they have a tendency to separate and the ember then only spreads along one piece, so if using this method use the biggest single piece of charred pith in your pile.