You can get out at any time, but it is subjected to GF confirm when you effectively can do it, due to the fact that they pay the rent at a three month basis. The GF contract is safer than an individual contract and it is haslle free regarding market soaring and you need to negociate the new contract with the landlord, who for sure will ask more for the apartment and will increase the rent in a annual basis.
If the rent falls below the new allowance you will not receive the difference.
That's it!