I purchased this brewer at a local shop in Brazil about 4 months ago, and brewed nearly daily on it. My first brews were uneven and made a mess on my stove. After quite a few bad brews and almost giving up on it, I began to understand what was going on.
I usually brewed finely-ground coffee and got mediocre results. I would, usually, fill the basket up to the top, tapping it just a little bit, and let it heat. Coffee would begin to brew unevenly, leaving me with a tiny extra-strong cup and a large extra-weak one. In other words, bad coffee. If I took too long to turn off the heat, there would also be coffee spills everywhere in the kitchen.
If you run a test brew with no coffee grounds in it, only water, you'll see it comes out perfectly even on both cups. I realized what the secret was after getting a sack of coarsely-ground gourmet coffee from a relative. Being coarser, the grounds would allow a free flow of water even if I filled the basket up to the top and tapped it. That way coffee would come out perfectly even on both cups. Coarse grounds give you a milder brew, but that's a matter of taste.
Learning from that, I realized that I couldn't fill the basket up to the top with finely-ground and tap it. Water wouldn't flow evenly and coffee would come out wrong.
Nowadays, I usually fill the basket leaving about 2-3mm free space at the top of the basket when using finely ground coffee and progressively less free space the coarser my grounds are. That leaves space for water to flow through more easily, making evrn cups of coffee.
That's a peculiarity of its unique design. There's a limit to how strong your coffee can be, and that will depend on the grind and toast of the coffee you"re using. A regular stovetop won't be limited by that, but it also wont' look this charming to a visitor.
In my opinion, this is the most charming way to enjoy a cup with your coffee-loving significant other. Great value, as long as you learn its ways.
**Regarding the coffee spills, it's all about timing when you turn off the heat. I turn it off just before air begins to come out of the coffee machine, that is, just before it ends brewing. I set the heat to minimum, wait for it to brew and, very few seconds after the brew begins to come out in a very light yellowish tint, turn the heat off. That's just before the brew ends. This reduces coffee spills to nearly zero.
Definitely NOT a novelty item!!