Steel tongue drums were created a few years after the birth of the Hang. They are also known as tank drums, hank drums, butadrums, butagongs, tongue pans, space drums, UFO drums, [whatever]drums...
The term "hank drum" was coined by Dennis Havlena in 2007, after "hang" and "tank". His goal was to create a much cheaper and affordable instrument than the Hang, that would produce similar sounds. He built his drum with an actual propane tank, hence the name "tank drum". Some makers have kept this approach, but others use their own materials and techniques, so this term can be a misnomer.
Unlike handpans, most steel tongue drums are sturdy enough be played using either hands or soft mallets, with rubber or cloth tips.
This means you can play more violently on a steel tongue drum, and even cut your fingers doing so. One can say that while both instruments may have similar sounds, steel tongue drums have a harsher spirit. You will take a beating, not the instrument, which is rather different from the softness required by a handpan.
There are many different kinds of drums, from cheap instruments made with propane tanks, to high-end drums that can look and sound a lot like the Hang, or within a league of their own. Some are built by hand, others by industrial processes. They're made all over the world, and price and quality can vary a lot.
The market is also quite diverse. Professional and hobbyist musicians use steel tongue drums, but anyone can also enjoy them for relaxation, meditation or music therapy. It's quite simple to find low-quality instruments on various e-commerce websites marketed for these purposes.
Things get even more complicated when drum makers name them differently to set themselves apart and build their brand, not to mention they can also sell handpans. Last but not least, tongue drums made of wood have been around since centuries, even if they look and sound very different and are usually referred to as "slit drums".
I fell into the steel tongue drums rabbit hole unexpectedly in early 2019. After a bit of research, I got a Rammerdrum 9", then more recently a RAV Vast. Here's a old blog post about me choosing my first drum.