Is bundling worth it, or does the box just get bigger and more expensive?

Usually it does, for two reasons: you pay one label and one handling instead of three, and your country clears one shipment and so charges the fixed clearance fee once. Carriers use volumetric weight: a large light box counts heavier than it weighs. That is why when bundling we do not put three boxes in a fourth, but take the items out of the outer boxes and pack them as compactly as possible into one new box; you do not ship the shop's air. In the calculator you see the difference in advance: enter the dimensions you expect, or wait until the parcels are in and compare separately versus together with the real dimensions. With two small parcels to a nearby country it sometimes saves little; with three or more, or to a far country, almost always a lot.