You also have to remember the application that website was using it for was for computer stuff which necessarily does not need to be water-tight.
Who knows it might work for something small, But once you want to do something big I dont know if its worth saving a couple bucks on the adhesive. Any way acrylic is pretty expensive, so if your spending money on acrylic sheets then might as well just shell out a few bucks more and know the stuff youre using is no going to fail.
Good find though because I have some scrap acrylics which I might use to build fan holders using this adhesive technique.

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90 gallon tank with center overflows, 44 gallon custom sump/fuge, Tek T5 retrofit 4x54 bulbs, Reef Octopus nw200 protein skimmer, Iwaki WMD40RLXT return pump (changed to panworld 100pxx),Knop c ca reactor, PA light house controller.
Click: Real-Time Stats 
^^ Testing it out! Ill add more param.. later.