I don't think they're claiming this as a "speed reading" product in the traditional sense. They're saying it increases reading speed when reading the way most people do, which is line by line. It's certainly not likely to be useful for the kind of reading where you need to scan. But for fiction and other writing that is meant to be read linearly, the claims they're making seem plausible.

What it doesn't help with is transposing from adjacent lines when reading the middle of a column, which happens to me all the time. The middle of the column is always black, so there's not much of a cue to keep you on the same line.

In making my workaround to get a similar effect in calibre, I made a variation I much prefer which cycles red->green->blue, so that column centers are always easy to separate.