Well on the Tankstick on my Arcade cabinet I use the bottom 4 buttons for shoulder buttons when needed but, more importantly, I use them for the universal exit configuration in GameEx.
On the Solo? Pretty sure there are a ton of buttons to configure them to.
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EDIT: I forgot about my Super Kuma 9000 case! Came in yesterday and I had it up in 10 minutes. Case includes a custom board that connects to the GPIO which adds functional Power and Reset switches. The shutdown script installed fairly quickly. I REALLY like this thing! Only $19.91 on their homepage and Amazon.