Business customer at Sixt = Kilometer flat rate or 1% regulation?

Hello, I have a question, because I am not quite sure about this… I plan to use a leasing as a commercial customer at SIXT. I am independent and can also “prove” all this by means of a business license at SIXT. Now it is the case that I want to know if in this case you have to park the car by means of 1% regulation even later OR if I can still write off even after purchase on the so-called mileage flat rate. I ask therefore, since there are already advantages, if one as a business owner However, the 1% rule is not worth it for me. Therefore, I would like to assert the kilometers with the FA after the purchase as a trader. The ratio does not allow me to make the 1% regulation and on a “yearly travel book” I have now best. no desire. Therefore the question whether the purchase as a trade is involuntarily connected with the 1% regulation or travel book method OR if I can then simply continue to apply the mileage flat rate. Is there tips to give? Thank you in advance Janwill