There's no obvious reason that won't work in your eMac--it specs out just fine.
That said, the reason for the price difference is the 90-day warranty (well, that and the "Limit 1 per Household." pretty much says it's a come-on to attract customers, maybe even at a loss). Any reasonable RAM brand offers a lifetime warranty--I use either Crucial (overpriced on that partciular chip at $120) or DMS when it's a lot cheaper (Datamem.com; $80 for the same), both of which will replace your stick if it ever goes bad.
Admittedly, this is a rare occurrence with RAM, but the 90 day warranty makes me wonder if it's not more prone to issues to begin with. I can say I've never had a Crucial or DMS stick fail out of dozens bought over the past 7 years (at work).
Hey, for $30 it's probably worth a shot.