If you've spare cash lying around why not buy the LTE router outright for R4200 (Includes Go Big 120 data - 60 gig can be used between 7h00 - 23 h 59 the other remainder data from 00h00 - 06h59 test the service. Prepaid is cheaper in the long run. If contract is your thing then go for it.
You can also get Telkom Mobile to send out a technician to test the signal before being committed to any contract.