That's interesting that it has the seal in the kit! I haven't seen those since the 1980s. Maybe I should get one: mine is all cracked and split. It's there to keep grit out, because the OEM bearings were only sealed on one side, and the sprocket bearings wear the fastest - maybe because grit gets in behind them?
My local bearing house gets between $7.50 and $9 for those size bearings in 2 seals, so other than the added shipping, that doesn't seem too bad at $28?