The Flirc USB controller is primarily meant for HTPC. While it may work with the Raspberry Pi, it’s important to note that the Raspberry Pi does not have on-board power management. That means–even with the Flirc USB connected, you’d still need a script (usually python) injected into the system to properly interpret the IR on/off command as Pi wake/shutdown.
At best, there might be code within the Kodi app that allows for this with the Flirc USB connected, however (1) I’m just guessing that such is the case, and (2) if it IS the case, you’d need to navigate to and launch Kodi (then pick up your remote and point it at your stick) every time you wished to shut things down.
The method I shared with the Sanwa (or Seimitsu) button, two wires and a python script are the most practical means to facilitate boot/shutdown. ETA Prime’s videos that I shared have a text description with a link to the text file that’s needed. It’s just copy, paste, enter, wait, repeat down the list. I’ve done it like 7 times already. It’s foolproof.
I have my case already with a button installed. It works great with the script.
Having an arcade button wired remotely to the Pi and mounted on the stick case is a more elegant option, though you could just get one of these cases and tuck it into the stick like was previously mentioned.