I've read a lot of the threads about this media this week because I'm looking at getting the ceramic blocks.
Some users noted their leathers closing up within hours of adding the ceramic blocks. For this to occur they either had a faulty manufactured block or, more likely, they didn't rinse the block before putting into the tank and any manufacturing dust or dust created while shipping (eg block rubbing against freight container) is what cause the aluminium spike.
Randy proved that over time the blocks leach a form of aluminium that is picked up by a Triton (ICP) test but never proved if the form of aluminium (possibly alumina) in the water is actually harmful or irritates coral, which I find a bit unusual as he spent a lot of time on the tests but only technically did half of them.
After reading it all, I am going to use them and if I see any adverse affects I will take the ceramic blocks out. I think it will be fine, if you do regular water changes you will more than likely keep the aluminium levels manageable even if they did appear.
Users who reported high aluminium levels never mentioned any other contributing factors, such as other aluminium in their tank (could be as simple as a washer somewhere, or other ceramic media), if they did regular water changes to export the aluminium, etc, so you kind of have to take it at face value.
Plenty of people use these blocks with no issues.