Leasing at Sixt instead of used cars?

Hello, I have been looking intensively for cheap used cars. However, the insurance costs would be very high with me. I noticed the complete package of Sixt. Sixt offers as I understood a comprehensive insurance for a lump sum amount. In addition, I found there really attractive leasing rates and wanted to ask you what you think about it? Skoda Citigo 1.0 MPI 60PS incl. tax, insurance and maintenance for 150€ per month (36 months 10tkm/p.a.) Alternative is the car also available as a natural gas version for 200€ per month. What do you think about it? Have I overlooked any costs? Which costs come roughly for transfer to me? Did I understand this correctly with the insurance?