You could view the information available on this link and also ask an agent if necessary https://support2.giffgaff.com/app/ask/Top-up-balances-and-goodybags/Buying-a-£20-goodybag/
You can expect to receive a reply to your question within 24 hours. An Agent will then reply to your question within your My Questions area.
What is 'Always On' data?
Our Always On goodybag is designed to give you peace of mind that you'll always have access to data. With Always On* you get 9GB of UK data usage per month at full 4G speed. Once you've used up your 9GB data allowance you will experience a reduced data speed of 384kbps from 8 am to midnight. From midnight to 7.59 am you’ll have a data allowance at full speed.
Tethering is now permitted on all goodybags, including the £20 Always on, before and after 9 GB of data. However, the Traffic Flow Policy and speed restriction still apply.