Considerations

Not fuel efficient in any trim: Both the 3.0 and 4.x, MT/AT have poor combined real-world fuel economy (sub 20 MPG)

Unreliable: Face it, the E53 is very unreliable. Plan on $2K (DIY) and 4K (non-DIY) per year on maintenance and repairs for a daily driver. That is using high-quality aftermarket and dealer parts when required. This includes brakes, tires, suspension, and repairs most likely needed at the time of purchase

Best practice buying process

Check CarFax for accident and (equally as important) service history. You can minimize your repair expenses if the previous owner completed expensive services and performed regular fluid changes.