Last time I checked, Redbull Mobile had a 200MB/month for 12 months deal at a cheaper price. That's 2.4GB for R49. If you have a decent Cell C 3G signal where you intend to use the internet, rather get that.
The 12GB special sounds good though. Cell C's R10 for 1GB night data that expires if not used within the 1AM-6AM window (if memory serves me right) and their R50 for 1GB midnight data that lasts 30 days can't compete with something that can be used any time during the month.
Overall, this is good news. Most South Africans buy legacy Blackberries because of BIS, though many probably use less than a gig a month. With prices like these, people can buy normal (non-BIS) modern Android smartphones and still do their Facebooking, Tweeting and emailing.