On a WSM I don't think you need one. Having said that, I would definitely get the DX2 over the Party if buying a Guru. And don't let the electricity scare you off. I use two 6 volt lantern batteries wired in series to power my DX2 when no power is available. I have about 16 hours of cook time on the batteries and they are still going strong.
BWS Party |UDS|Great Outdoors Propane Vertical|Maverick ET-73 |Maverick ET-732 |Super Fast Orange Thermapen | BBQ Guru DigiQ |Two 100 QT crawfish boiling rigs | LEM Meat Grinder | Grizzly Sausage Stuffer
Smokin-n-Style BBQ Team - Pitmaster
Lagniappe Chili Team - Head Cook