Huawei can support 150Mbps so why sold as only 20Mbps?

Hello, long time lurker first time poster,

Forgive if this is a noob question, but I see the Huawei E5573 mobile broadband dongle can support a 150Mbps download and 50Mbps upload, so why is it being sold on price comparison sites branded with iD Mobile and show as being limited to 20Mbps down?

Virtual network operators don't always get full access to the full speed of the native service, i.e. it is a way of the core provider who has its own retail services from being able to boast about faster speeds, since it limits some or all of its resellers.

Additionally it may be comparison sites are playing it safe when talking about mobile speeds and don't want to fall foul of advertising rules.