When it comes to a GoTo telescope, you need a computer. With the servo drive you can choose between a stand alone Argo Navis (AN) hand held computer or an old laptop computer you buy or have lying around. (For tracking only with a dob, you don't need either. The servo controller has it's own computer "chips" inside the little box just for that ).

A few notes about your choice: 

The AN is $850.00 from JMI or $544.00 plus shipping from Au. 
The AN uses small AA batteries
The AN is compact and purpose built. A very nice unit if you have the funds for one. 
Cables are extra. 
Encoders are extra. 
Where do you go if you drop it and it's damaged ?

A laptop on the other hand:

Can be had for $300.00 online at ATR computers fully loaded with XP .
Can use the same 12 volt battery used for the servo drive with a cheap power plug voltage adapter. 
Can be used for other things, like a full planetarium, imaging software etc. while using the servo software
The laptop is slightly bigger. 
The cable from the laptop to the servo controller is included with the controller purchase. 
Extra encoders are not required. There are encoders on the servo motors. 
The software, Sky Charts, DOT Net, ASCOM and the servo software are free downloads. 
There are computer repair stores all around. 
You do need a red screen cover if you are at a star party. 
 

The decision to use a laptop or the Argo Navis is completely yours. You CAN use one with the Servo Controller if you prefer.