When you say high cost, you talking about the 1.5" starter cubes? Cause where i get mine they are equal to or with in a dime of each other STG vs Rockwool.
Now i do have to say that there are a lot of hydroponic stores that are jacking up the prices on STG. To the point even STG was helping some friends start up an online store. I order'd my 6x6 from them and they sent me 4x4's, i went straight to STG after i couldn't get ahold of the internet ppl. They appoligezed and explained what was going on with that company and 1day shipped me replacement 6x6 cubes and told me to just keep the 4x4's.
I can tell you from my experience the starter cubes will suck up water very well. It's the bigger cubes that drain well. The 4x4 and the 6x6 drain well and allow good air flow.
Film showing there water density theory. Altho i haven't tried rockwool personally. After all the studying i did. A lot of ppl were complaining about them falling apart. I didn't know what they were talking about till i seen this clip. And i understand that each company is going to show you the pro's over the con's of the competitor it's the nature of the beast. And a link to there product claim.
http://www.suretogrow.com/hydroponic-supply-stg
Sure To Grow block water density - YouTube
One of the biggest things i went for with STG is it being neutral. And as you can see from the post i've started. The less i have to worry about stuff the better off i am.
Nother film of them using the starter cubes and how to put them in an NFT system.
Using Sure To Grow cubes in an NFT hydroponics system - YouTube
On a side note, just for the heck of it. I'm going to see how hard it would be to actually reuse these cubes i have tomato plant's in. More cause i'm bored and have nothing else to do.