"not suitable for bandwidth hungry activities" implies that attempting to to undertake such activities at a maximum of 384kpbs means that they will be compromised.
And you make things go slower by not allowing them to go as fast as they might otherwise i.e. by throttling the bandwidth.
If someone wants unlimited data, giffgaff is not for them, as giffgaff makes clear via the "Always on" terms and conditions.
I really am at a loss to understand the point you are attempting to make.