I agree, the sodastream machine is phenomenal... I drink seltzer almost exclusively, and before I had the machine I hated having to deal with all the empty plastic bottles. I'm not sure that soda stream has a huge cost benefit over buying seltzer when in bulk when it is on sale... but I like that it doesn't generate garbage and also I like fact that it is much more compact than storing a bunch of bottled water.

Also, to nitpick, I think club soda is not quite the same thing... I believe it usually has some sort of sodium or potassium salt while seltzer is just H2O + CO2 like you describe.

Not sure if the flavored bottle would even really be that effective... and $25 for the bottle seems kind of expensive just to be able to try it out, especially since this seems fairly simple to DIY.