Well written!
Lots of reviews and user comments mix up the Tengwar script and Elvish languages (Quenya, Sindarin)...
And I don't think many buyers even consider writing in Tengwar with this keyboard. It's just as an empty keyboard to them, with some cool devices that don't distract, and they have the normal US layout memorised, and use it as that.
There are many better ways of writing Tengwar than with a dedicated keyboard. There are transcribing tools on the net, and in form of programs and apps - writing in Tengwar means memorising lots of rules about uses of different characters (it's not just 1:1 letter replacement, even when writing English), tehta (wovel sign) placement, those transcribers help with that. And of course, you can always grab a calligraphy pen.
And neither Quenya nor Sindarin are "fully functioning languages". They don't have extensive dictionaries, they are even missing large parts of their grammars. So every time you're not just reusing sentences Tolkien already wrote you're forced to invent and speculate. That's why for instance David Salo called the language used in LotR movies "neo-Sindarin".