Well its better than any other deal out there. Its only available on the Telkom Mobile network so make sure you got good coverage by buying a smallish bundle first to test.
Its a good if you don't use the whole bundle in one month.
Lets say you get 12Mbps download speed and 2Mbps upload speed. So now you got 25GB with a +-12Mbps line. With mobile data you don't pay for speed but pay for data. So if you only need to use 25GB of data in 2 months it would be a better deal compared to ADSL. If you need to use more then it might be better to get ADSL.
R999 for 25GB + 25GB data @ +- 12Mbps download and 2Mbps upload *depending on coverage/3G or LTE and tower congestion
R125 axxess adsl account + R425 10Mbps adsl line rental monthly +- R150 analog rental monthly = R700 monthly for a ADSL equivalent
This is just a estimate very rough comparison of how the Mobile deal could compare to ADSL. ADSL is much more flexable because its not ISP limited and you can get much more data for cheaper. Setup fee's can be pricy for ADSL to have a brand new line installed. Mobile data speeds also varies and is coverage dependant.
So its hard to say but it would mainly depend on how much data you use. How fast you use it in terms of weeks months and what speed connection you want/need