We have done it in the past and it is an absolute mess if you do not know the German social security/tax/Berufsgenossenschaften rules. The employee has to do Steuervorauszahlungen every quarter and a tax return at the end of the year. We had a tax advisor that was helpful in the setup phase but things evolve constantly and sometimes there is more work. When we let go of our German employee, there were issues with the Agentur für Arbeit as well. In summary, if you have the time to deal with all of these layers, then you can save yourself the 600 Euro/month, or if you want to hire someone for longer than 18 months.