That is convenient. The 400% & 8000 gallon figures are impressive. Cheap it ain't- I can get a cubic foot of 12/40 mesh cgac for $106 off amazon, enough to refill 35 cartridges or $3 per cartridge. With retirement approaching I am becoming a penny pinching miser, lol. The Resintech MBD-30 DI Resin isn't so inexpensive- $9/refill in 5Lb bags (enough for 4 or 5 refills). The DI Resin has to be kept absolutely dry and preferably vacuum sealed until use so buying quantities of it isn't practical for me, but it's still way less expensive than disposable DI cartridges. I also got a really good price on the filter housings- Amazon was asking less than $16 each when I ordered them.