I use iBurst, and to be honest as long as you dont call their call center they're a decent service provide (lol?)
To answer your question, I was on the 10Gb offering, but although it was a decent offering, I actually increased to the 20Gb option so I could cash in on the extra 10Gb for only +/- R57..
Pros:
no line rental fee
cost effective
decent speeds (if in the right coverage zone, see cons section)
Cons:
calls to customer service call center will drive you nuts, try and avoid at all costs
very zone dependant - restricted to major cities only at the moment, and within cities some areas are better covered than others (see iBurst coverage map before buying)
can sometimes be 'spotty' in international connection (dunno why), but limited to around a few hours once a month