I once needed a diff for my skyline and I needed it before my scheduled inspection. The previous owner had contacted Osaka and got the quote and stuff, and my dad and I figured that if we saw them change out the diff, not much could go wrong. I was busy that day, but my dad drove the Skyline to Osaka and asked if he could watch them working on the car. They said no, which is pretty sketch knowing that they are basically a chop shop, so he just left. They called him back saying he could watch so we had the work done (we needed it in time for the inspection) and overall their work was fine. (cant get too much wrong just swapping a diff) The diff was also fine, but the oil in it was old causing it to lock on every little turn (its an LSD). With the new oil its perfectly fine so overall I cant complain about my personal experience with Osaka.
TL;DR Osaka sketched us out, but ended up doing good work in the end, cant complain.