This hoverboard doesn't have any unlockable upgrades.
Ukulele is the fifty-first limited hoverboard in Subway Surfers. It is a limited hoverboard exclusive to Subway Surfers World Tour: Hawaii 2017. Like any other hoverboard, it protects you from crashing for 30 seconds. When crashed, the hoverboard will explode and need to recharge for a few seconds before using again. The hoverboard is shaped like an ukulele. Like most of others limited hoverboards, it costs 50,000.
This is the second limited hoverboard in Hawaii, the first being Tiki.