"Tries" is the operative word here, really: Before Sentence Aerobics can recommend changes, it must correctly parse the original language--but it didn't succeed at that preliminary task when dealing with the simple paragraph that I fed it. The paragraph read, in part:

"What could possibly go wrong? As it turns out, quite a bit. [...] Spanning Backup ($3 per month for regular Google accounts users) is a cloud backup service [...]"

Sentence Aerobics circled the word accounts above in green, applauding me for using such a "Strong Verb"--but the word is used as part of a compound noun here. (A clearer formulation of the parenthetical phrase would be "$3 per month for users of regular Google accounts"; unless, of course, the intended meaning is "$3 per month for regular users of Google accounts." Admittedly, expecting a program to figure out that level of nested ambiguity is asking a lot of it.) The program also approved of the word turns in the phrase "As it turns out," failing to parse it as an idiom. Meanwhile, Sentence Aerobics asserted that the word could in "What could possibly go wrong?" was a "Weak Verb" in need of revision, rather than a necessary conditional auxiliary to the verb go in what amounts to a common catch-phrase.

In short, Sentence Aerobics' parsing is limited and error-prone, especially in dealing with idioms. Competing product is less susceptible to such errors: It let the same exact paragraph slide with no recommendations, other than noting that one line has a high "glue word" count.

Once Sentence Aerobics finishes parsing your text, it offers recommendations. For the most part, its advice is sensible: Sentence Aerobics favors short, active sentences, and tries to trim prepositional phrases from the text. But since its parsing is often faulty, you end up with many recommendations that you can't implement. For instance, when I started a line with "It turns out this is not a bug," Sentence Aerobics told me that starting a sentence with the word it is not a good idea, since the reader may have trouble figuring what it refers to. But this generally sound advice again misses the mark due to poor parsing.