Looking back at the Polt collection, the earlier Gromina (right) is also flat and fetching, but I gave it a D for typing feel. Not a pleasant typer.
The same holds true for the French Rooy, which inarguably fits the description "laptop" if we just go by its astonishing flatness and built-in sliding case. You don't buy a Rooy for typing, you buy it for the novelty and coolness factor.
A decent alternative might be one of the Hermes small portables (Baby, Featherweight, Rocket, Empire Aristocrat, etc.). Compact though not as as thin, it will not win a beauty contest against the Kolibri, but it does have a slight advantage in terms of touch. It also weighs less. Unfortunately, my long and thin fingers type clumsily on a Hermes Baby.
Two popular alternatives in the U.S. are the Olympia Socialite (Splendid) and the Smith-Corona Skyriter. Typical of Olympia, the former looks neat and types pleasantly, although I have an issue about the tinny noise it makes because of its metal base. I've never typed on a Skyriter but I would guess that it has the signature Smith-Corona springiness. Since it also has a metal base, I wonder if it types noisily as well. I know Bill M. owns several of these so perhaps he can fill me in. My one quibble with the Skyriter is that it comes in fifty shades of dull grey.
Image: Machines of Loving Grace
Of late, the Princess 200 (Scheidegger Princess-Matic, Maritsa 11, etc.) is one machine that has caught my eye. It looks great, has gotten good press in terms of typing action, and is easier on the pocket than the Kolibri, that is, if you are lucky enough to find one. Some have mentioned that it is a loud typer, but we know that a good platen could address that. The catch: it weighs 13 lbs (6 kg)! I usually travel light so I'm not sure I'd welcome excess baggage, even if she's a princess.
* Typo correction: "sea
* SC Skyriter image: Etsy
* Typecast via Olivetti Lettera 22