I know it is a sugar alcohol but how does it play into the Zone diet? Better than the real thing? Worse? Should one be eating this while trying to maintain the balance of the Zone?

Dr. Sears doesn't recommend eating sugar alcohols.

Dr. Sears doesn't recommend eating sugar alcohols.

However, Erythritol is different from the other sugar alcohols, and might not have existed when Dr. Sears evaluated.
Erythritol, unlike other sugar alcohols, is fermented in the process.

Erythritol occurs naturally in small amounts in some fruits, and in greater amounts in certain mushrooms and other fungi, and in fermented foods such as wine and soy sauce. The form used in foods is generally made by the fermentation of plant sugars.
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At the industrial level, it is produced from glucose by fermentation with a yeast, Moniliella pollinis.. It is 60–70% as sweet as table sugar yet it is almost noncaloric, does not affect blood sugar, does not cause tooth decay, and is partially absorbed by the body, excreted in urine and feces. It is less likely to cause gastric side effects than other sugar alcohols due to its unique digestion pathway.
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In the body, most of the erythritol is absorbed into the bloodstream in the small intestine, and then for the most part excreted unchanged in the urine. About 10% enters the colon. Because 90% of erythritol is absorbed before it enters the large intestine, it does not normally cause laxative effects, as are often experienced after consumption of other sugar alcohols (such as xylitol and maltitol).
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It can be used in baking, where it also has some of the tenderizing effects of sugar (results won't be exactly like sugar, though). It can at least partially replace sugar or artificial sweeteners for most uses. It is especially useful in combination with chocolate (candy, brownies, etc.) where using purely artificial sweeteners produces unsatisfactory results.
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In general, erythritol is free of side effects in regular use. When compared with other sugar alcohols, it is also much more difficult for intestinal bacteria to digest, so is less likely to cause gas or bloating than other polyols, such as maltitol, sorbitol, or lactitol.
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There's a popular product out there (can't mention it or I'll be banished) that uses Erythritol, along with Stevia and some other natural stuff, as a sweetener and it definitely causes less GI discomfort (for me) than the other sugar alcohols. And doesn't feel at all like it registers as a carb...

I believe the other natural stuff is Inulin, a fiber, used as a carrier and to help bulk it up so that 1 tsp is equivalent to 1 tsp of sugar in sweetness. Otherwise, without it, 1 tsp would be an awful lot of sweetness!
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(I used to take 1 Tbl of Inulin years ago, before starting the Zone, as a fiber supplement because I was not eating a lot of vegetables, hardly any, and a little fruit pre-Zone days - so Inulin worked well as a fiber supplement. It mixes well and clear with water and with a lot more than the 3g fiber per serving that that of Metamucil, et. al.)