Overall, great experience.
Initially I was skeptical due to the incredibly low rates, so I had alternate plans in place just in case things went south. However, the whole experience was very smooth! A couple of observations:
1. The Sixt Rental Location is far from the other companies (Alamo, Avis, Hertz, etc.) at DEN.
2. Interacted with 2 employees (1 Rental; 1 Return). Both were very friendly and helpful; A++.
3. Vehicle was very nice. Booked a Premium SUV and got a M-Benz GLA.
4. The required deposit was very high.
The only unknown at this point is the deposit return. Will update when I receive the deposit refund back onto my credit card.