Canamonster .......... In Canada there may be even a better product than SeptoBac. I'm just currently trying it out now. Bactri Pond, which is manufactured by Canadian BioSystems, just south of me in Calgary.
http://www.evenspray.com/Spec sheets/Bactri-Pond - PKG0309.pdf
It's designed for ponds, and contains Bacillus sp. bacteria, which is what most of these products contain in some form or another. Bactri Pond comes in a foil type re-sealable bag, that contains 50, 10 gram soluble white powder packets. Each pack treats 6,300 gallons of water. The beauty of this product is that it is VERY soluble in water, no need to premix, and no added bran fillers etc that one finds in the septic tank products. It's like adding a pinch of Seachem Safe to your tank, it dissolves on contact, and a little goes a LONG way.
I bought mine at a local hardware store, on end of season sale for $33.00
http://peaveymartonline.com/index.php?route=product/product&product_id=338
50 packets, x 6,300 gallons = 315,000 gallons of tank water that one can treat.
As Duane mentioned, the real beauty of these probiotic bacteria is they also outcompete many of the "bad" bacteria, such as the ones that cause serious health issues in ornamental fish. As well as other forms of bacteria, such as the ones that create green/blue algae. (cyanobacteria)
IMO probiotics are simply another tool that a hobbyist can use to keep their system running problem free, while also allowing one to cut back on some of the regular maintenance.