apc sucks. A filter is not just a filter. 2 things a filter is designed to do. That is make as much air go through it as possible, and trap as much dirt as possible.
There was a test of many diffrent filters. The top two were K&N and Apexi, resulting in the best flow and dirt trapage.
As for strut bars, stiffness and mounting location is key. A while ago, DC strutbars were horrible, and would actually bend with the littlest of pressure. I leaned on one in a 7th gen civic and with almost no pressure to it, it flexed. That does nothing for structual rigidity. Also, if the bar is hinged, its going to keep the strut towers from moving in and out, however will not stop them from moving up and down. Good brands are nuespeed, mugen, carbing, ect.
As for coilovers, they are designed like crap, will bounce all over the place, and give a shitty ride with zero performance.
A header is not just a header. Quality effects the performance and the realibailty a shit load. A hytech header has been known to give gains of up to 19hp on a basicly stock ITR. If a header is designed like shit it will give zero or 1 hp gains.
For seats. I would hate to be in an APC seat in a crash. Structual rigidy of the seat is key for safty. If a support in the seat give loose during a crash, you just got speared. A Sparco seat is certified, APC is not.