In general, I've ordered all sorts of non car stuff from abroad and never had a problem.

Germans I've found are particularly easy to deal with and very reliable.

I've only bought a couple of things from Negun, but they seem to have a pretty good reputation among Japanese car enthusiasts, and I had no problems with them.

Their paperwork also came in English, so no need to reach for Google translate.

My filter came via Fedex, who invoiced me for the import charges prior to delivery.

But it did take 6 weeks to arrive from Japan, and could be longer in current circumstances.

The actual Apexi installation instructions will probably be in Japanese, but I used an installation guide, linked below, which is for fitting it to an MR2 with an AFM, and is also very comprehensive:
Installation Guide

Hope that helps.

Paul