With so many people practically living in their Gmail accounts, it's a surprise that the third-party peripheral industry has taken so long to come up with a standalone shortcut pad for the popular email system. The Gboard has a similar form-factor to a USB numeric keypad, but rather than numbers it offers eighteen shortcuts (and an escape key) that give Gmail's keyboard shortcuts dedicated buttons.
The most commonly used commands are present, including starring and spamming messages, trashing them, reply/reply-all/forward and folder navigation. The latter not only allows you to step through messages one by one, but also to jump to saved search results or view only starred emails.
Compatible with both Windows and Mac, the gimmick is that it's all plug & play so setup shouldn't present any problems. By the same stroke, it doesn't look like you can remap the Gboard buttons, so if you want them to do something different then you'd probably need to remap the shortcuts in Gmail itself. The Gboard is available this month, priced at $19.99.