I'm sure the Surley 'Singulator' as shown above, works nice and is a simple fix, but one of the big attractions of SS to me is the simple, uncluttered look--------adding a tensioner is going backwards, in this regard! I'd do everything I could to avoid having to use one, including looking for a different bike with horizontal drop-outs. My thoughts on the Eno hub are that I'd have to really like a frame to spend that much in order to get chain tension. No doubt, it's very cool and preserves the clean 'look', but that much $$ for a hub would be a good down-payment on a complete new SS bike! :S
I also just wanted to add----for any other first-timers out there-----with a dedicated SS ring and sprocket and careful chainline alignment, you might get by without having as tight of tension as you'd ideally like! Just try it----as I said, I've ridden bike hard for many hours now and it shows no sign of dropping the chain. Beginners luck, I guess!! Sadly, when I tried to put a cog just 1 tooth bigger on, it made it too tight.