384kbps after you have used 9GB of data is quite slow. Also be aware of the Traffic Flow Policy which could affect you if you are a high data user. Mobile data is meant to replace your home broadband.
Always On data
With Always On you get 9GB of data at full 4G speed. After 9GB of data used you'll experience a reduced data speed of 384kbps from 8am to Midnight. You may notice that activities which require high amounts of data, like HD video streaming, will be slower.
Traffic Flow Policy
In order to protect the experience of our members when they are using data on giffgaff, we have introduced some measures, which we call Traffic Flow. This article explains these measures, how they will improve the experience for the majority of members and how you can avoid negatively impacting the data experience for other giffgaff members.https://community.giffgaff.com/t5/Learning-and-giffgaffer-articles/Traffic-Flow-Policy/ta-p/12999304