hanc310: "So, does a washlet add much more height than a normal toilet seat? If so, how much? And, is there a difference with brand -- specifically between the Toto S300 and the Bio Bidet 1000? And, just fyi, I'm contemplating the Toto Drake II as the ADA toilet. Unless somebody knows something I don't."

An advanced or "shower" toilet seat ("Washlet" is a registered trademark of Toto) will add a little bit of height to the seating position, but not enough that you are likely to notice it; the water tank is usually behind the seat, and the plumbing inside the seat proper fills space that most toilet seats have anyway. You can get exact specifications (usually as .pdf files) for most of the shower toilet seats through Terry Love's site.

I am not sure whether your question about differences between brands was limited to your topic of seat thickness, or whether you wanted other differences addressed, but (if the latter), yes, there are functional differences among brands.

Two important differences (related to each other) are the angle at which the water stream sprays upward, and whether the posterior and feminine sprays are delivered from separate independent spray wands or from separate nozzles in a single dual-function spray wand.

Inax, Japan's second largest plumbing fixture supplier and the inventor (yes, before Toto) of the category, is an R&D pioneer, and decided from the beginning -- after research but with no competitor's model in existence to use as a template -- that the ideal angle of incidence for posterior cleaning is 70 degrees from horizontal (i.e., 20 degrees from vertical). However, a spray wand that is positioned to deliver the stream at that angle for posterior cleaning is not well positioned for feminine cleaning, so Inax shower toilet seats historically have used two separate wands, one dedicated to posterior cleansing and a separate wand dedicated to feminine cleansing.

Toto decided early on to use a single wand design, with separate nozzles within the single wand for posterior and feminine functions. The constraints of making the wand serve dual functions require that Toto Washlets direct the posterior cleansing stream at 43 degrees from horizontal (i.e., 47 degrees from vertical). Because of the different angle that the spray hits its target, Washlets cleanse differently from Inax shower seats.

In commercial applications in Japan (airports, hotels, restaurants, etc.), you will see only Toto or Inax brand fixtures; we travel to Japan about twice a year and have looked into (as it were) and compared the latest toilet seat models in the Japanese domestic market; and I cannot recall seeing a shower toilet seat of any brand other than Inax or Toto except in a box in a retail store.

FWIW, when we recently purchased a toilet and a shower toilet seat for one of our bathrooms in our home here in the U.S., we chose a Toto Vespin II (the skirted version of the Drake II that you are considering) toilet with an Inax Clessence shower toilet seat; yes, they match.

Here is a link that might be useful: Page with some links to spec sheets for shower toilet seats