Rammerdrum is an Italian maker of steel tongue drums, handpans and kalimbas. Their drums, named "harmonic discs", come in four size : 9, 12, 15 and 18 inches.
The Rammerdrum 9" is one of the smallest steel tongue drums in existence, but offers a great sound despite its size. It's an interesting choice for beginners or children, or people looking for a highly portable instrument, as it can be played with one hand while held in the other hand.
Its main drawback is that it has only six notes, and no ding (the central, lowest note usually found at the top) This limitation, while theoretically making the instrument simpler to play, also means that the traditional playing techniques using eight or nine notes need to be adapted.
My first steel tongue drum is a Rammerdrum 9" Akebono, and it was a good choice for my budget. I could have chosen a bigger drum for the same price, but after comparing lots of instruments for a couple of weeks, its sound quality and its primal aesthetics really stood out.
However, if you're a beginner and if your wallet allows it, I'd recommend getting a drum with at least 8 notes and a ding. You'll find many more learning ressources for this layout, which is kind of standard for handpans and steel tongue drums.