Giant Business Connect (GBC) as a Deemed Employer is different to their other business - Giant the Umbrella Company.
A Deemed Employer is a way for PSCs to take inside IR35 contracts without having to change their business structure. So it handles the very specific IR35-related tax obligations that relate to that individual assignment. This route does not provide benefits like a traditional employer such as Statutory Sick Pack and Holiday Leave. Deemed Employment is ONLY about tax - and only about IR35-related tax.
Giant the Umbrella Company are an employer (for employment law and tax). As such, you are entitled to statutory employee benefits (along with any other benefits they choose to award their employees) and you are subject to ordinary PAYE arrangements.
And just to be absolutely clear - you are under no obligation to change your structure, or join an Umbrella company. However, If you wish to continue providing services via your PSC in an Inside IR35 contract, you must have a Deemed Employer.
See how the Giant Business Connect as a Deemed Employer works here.