This sounds like a specialist Umbrella
Contracting Services by Chesterfield Group
How did you get involved with them?
Was it via the agency providing the contract if so were they on their PSL or something?
I would suggest you check what their Margin is as it could be way more per week/month than those of us paying to a 'normal' brolly in the UK.
If it is expensive that probably reinforces the advice already given, use a local accountant in Hungary.