Google Analytics using "Keys for external services" versus custom HTML head

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It seems like there are potentially two methods to do Google Analytics tracking for an Askbot site. The obvious way would be to put in your GA tracking id or key in the "Keys for external services" settings page--and that totally works; I've tested it. But the other way would be to put the GA tracking code script in your custom HTML HEAD on the "Skin, logos, and HTML parts" page.

Does anyone know what the pros and cons are for each method? Does the custom HEAD method work equally well?

When I have tracking turned on using "Keys for external services", I don't see the GA tracking script in the HTML source of a given Askbot page when I look at it. So I don't really know how it's working. I guess it's possible that Askbot is doing more in it's GA tracking request than would be available from the custom HEAD. Anyone know what Askbot is doing internally?

A final complication is that GA is now upgrading its tracking to "Universal Analytics" which involves changing to a different tracking code. Is that a good reason to use the custom HEAD method instead?