Reasons for Iron Core Inductors
There is a common belief that iron cores are inferior to air core inductors. To an extent, that is true. But an iron core inductor used well below saturation will exhibit distortion levels orders of magnitude lower than the drivers they're connected to.
With the prices of copper these days, keeping the price of a passive crossover low almost mandates the use of iron/steel/ferrite as an inductance booster to lower the amount of copper required to achieve the desired result. The lower in frequency you go, the more it matters since the part values become quite large and expensive. Price out a 6mH air core inductor of 15ga or lower and you'll get a real shock.
The kit comes with many options, including one with no crossover, allowing the builder to simply use the accompanying schematic to construct the crossover with the parts they like the best. Low gauge air core inductors, boutique caps and metal film resistors may, or may not help in the overall production of sound, but it's a sure bet that the wallet will be a lot lighter.
The intention of the Schumakubins is bang for the buck, and a big sound in a small footprint at a low price. On that account, they really do shine. Crank them up and you'll really get a shock when you realize that those smallish 7" woofers are producing that full range sound.