Don't jump to conclusions too fast 
There might be a number of reasons for which they sell 5-packs of filters.
One would be that it is VERY easy to lose a stone as it is in no way fastened to the Health Stone pipe or bowl.
Just turn it upside down and the stone falls down.
Another reason might be HSG advises to use triple flame jet torch lighters in order to get the whole surface of the stone hot at once, in the case of cannabis oil.
That might shorten the stone's life span, although I think the ceramic material is supposed to take even higher temps than a triple flame torch allows.
And a third might be that probably most oil extractors don't clean their product very well so it might leave some residue that end up clogging the filters by particles that won't dissolve with alcohol/cleaning agents. Though maybe with some compressed air...
The stones material look identical (but bigger) to the VG ones.
True, though, for the price of 1 Health Stone, I can get a coil VaporGenie with its stone with international shipping included...
We'll see in the long run, I guess.
Check out my thread here : Health Stone Glass Handvape experiment - Vaping/Smoking - Welcome to the DMT-Nexus
PS: Now that I come to think of it, it might be a good way to vaporize bufotenine... I'll keep you informed on that one as I have an extraction going on right now (IPA + MEK:heptane)