The way I see it having done Umbrella, Direct, Self Employed etc
The upside with Umbrella Companies/Agency you get to offset your expenses against tax.
Agency; No Holiday, no employment rights, offset your weekly expenses to cover employers NI, employee NI, and your tax
vs Employed (on the books), Full employment rights, 20 days and Bank holidays holiday, pay your own NI and Tax, Employer pays Employers NI, claim expenses back at the end of the year anyway, even if not as much as when Self Employed for a firm.