That said, why not go with the ORIGINAL bidet seat: the Toto Washlet? It is expressly advertised as fitting on any standard toilet. Folks in Japan have been using the washlet seat for decades. See the selection at totowashlet.com or totousa.com Toto also makes an expensive toilet with a built-in Washlet known as the Neorest. Very popular in Japan, and appearing more and more in high-end bathrooms here in the US.
Actually, the ORIGINAL advanced toilet seat was introduced in Japan by
Inax about a year before Toto introduced the Washlet. Toto realized the seriousness of the challenge that Inax's initiative posed, and was seriously concerned that it (Toto) would go out of business before it could get into the game with its own "shower toilet seat" (as they initially were called). The story is told in more detail in Rose George's book,
The Big Necessity.
Fortunately for Toto, at that time, only about 30 percent of Japanese homes had Western toilets; but the percentage was expanding rapidly during the economic boom, so there was a big new market opening up. And then Inax had a total
disaster of a television commercial for its version of shower toilet seat that almost took Inax out of the competition altogether; you can see the Inax commercial on YouTube here:
Toto, for its part, introduced the Washlet with a television commercial starring the Japanese equivalent of Cindi Lauper (Jun Togawa), which you can see here:
The Toto ad was a HUGE hit, Washlet sales took off, and the rest, as they say, is history. The Toto
vs. Inax television ad campaigns went on to become a standard object lesson for advertising industry textbooks.
Returning to 2012, there remains an important difference in design philosophy between the Toto and Inax toilet seats. Starting from a clean sheet of paper (as it were) to design the first entry in the category, Inax determined that the cleansing stream to the posterior optimally should spray at 70 degrees (from horizontal) -- just 20 degrees away from vertical -- for maximum cleansing effectiveness. Positioned as it needs to be to spray at that angle, the wand from which the spray is directed is not well positioned to use the same wand for a "feminine" cleansing function, so for the feminine cleansing function, Inax uses a dedicated second wand optimized for the purpose. Toto, in order to get by with using a single wand, positions the wand to spray water toward the posterior at 43 degrees from horizontal, actually closer to horizontal than vertical; with the wand so positioned, a separate nozzle on the same wand can be used for feminine cleansing. That 27 degrees of difference in spray angle is a difference that makes a difference.
Having tried both Inax and Toto toilet seats in Japan, when we purchased an advanced toilet seat for our Toto Vespin II toilet in North America, the model that we purchased from Terry Love was the Inax Clessence.