It's only expensive if you buy it off the Market Board.

If you craft it yourself, you'll save at least 500k gil on my server, that's half the cost.

If you get your own sealants, you cut off almost 90% of the price.

And the reason I got mine is because it's a (very small, yes) boost on all my 3 gatherers and I don't have to have 3 sets of equipment.