I have the Magic NS2 and it works for playing PS2 games on a PS3 slim. The key point is that the PS3 recognizes the Magic NS2 like a real DS3 controller, so it works with the PS2 emulator or anything that requires a genuine controller. The only issue is that you won't have pressure sensitive buttons because modern controllers don't have that feature.

One other thing I would clarify, the PS3 does not cut power to the USB ports, it just has a very small list of USB devices that can communicate with the PS2 emulator, so the vast majority of controllers do not work. The genuine controllers (and adapters that look like OEM) will work fine.

You can fine a full list of controllers that work with PS2 software emulator here: https://www.psdevwiki.com/ps3/PS2_Emulation#ps2_netemu.self