Spritz is a very interesting application. Although I agree that it does have some very useful uses - especially on limited-screen personal mobile devices such as Pebble or other SmartWatches, its application to speed up conventional reading may be less than appropriate, even when effective. And undoubtedly, it is not the only technology that may bring unintentional consequences with it in the process of bringing out some benefit.
How Spritz works
Conventional reading: When reading, only around 20% of your time is spent processing content. The remaining 80% is spent physically moving your eyes from word to word...
Spritz does two things differently: it lines up the optimal recognition point of words, and flashes words to the reader according to the rhythm of reading, which includes natural pauses.
Why should there be concern?
Chronic health problems are emerging at an unprecedented rate. This is quite likely linked to the emergence of digital technologies and the resulting transformation on our daily habits. For example: too much desk work leads to back problems, chronic pain, and bad typing posture leads to carpal tunnel syndrome. Eye fatigue is a known condition, where eye muscles become strained and certain muscles 'stiffen up', just as you may have one index finger noticably stiffer than the other due to overuse of your touchscreen smartphone. As eyes are one of the most sensitive organs we have, I'm not certain that stiff eyes and tunnel-vision syndrome are worth the tradeoff for faster reading.
My point, though, is not that eye fatigue is going to come onto the list of health issues to watch out for. My point is that novel technology - regardless of the benefits it brings - may likely have some negative side effects, and these side effects are usually not listed in the marketing prospect. And as community, we have an ethical responsibility to think these things through, and lay open the consequences in a transparent manner to allow everyone to make informed decisions on the expected tradeoffs when jumping onto any one bandwagon.
Finally, for the record: I think Spritz is a great application, and I think it is worth taking a look at. Even if it is not the perfect tool for healthily reading large texts, it is great for occasional, urgent reads such as an SMS, a voice-to-text answering machine recording, and triaging mails or messages on your watch or in Glass. It will be exciting to see how their application market unfolds as personal computing devices become smaller and ubiquotous!