Just FYI, this isn't the "Ask Greg Covey Show." No offense Greg.
This is a forum where many people ask and answer questions, and the ones who answer questions (like me) might be a little insulted that our expertise isn't "good enough" when you address your query to a specific person. :disappoin
You can look up what comes in a Slow Stick flight pack, and compare it to the JR 537 servo at
http://www.horizonhobby.com. IIRC, it comes with two GWS Naro servos. The 537 is a standard servo, a good ounce or so heavier. On a 13oz plane, that's a lot of weight. However, the Slow Stick has a few ounces of payload capacity, as evidenced by people hauling cameras, large batteries, and full size radio equipment aloft on the stock power system.
Still, if this is your first airplane, or first electric airplane, I suggest you pick up the GWS flight pack for it, or at least take a look at the contents. You can then see what equipment it takes to make an electric plane fly successfully, and can make educated equipment choices in the future.