The big issue with the roof rack is lifting the things in position without scratching the car. When lifting these things to head height, they are more clumsy to place, and this means that it will always be your job to put them up and take them down.
To demonstrate this to yourself, lift one of your bikes into position over your car, to give yourself an understanding of how you've got to do it.
Which is fine if it's only occasionally but is a faff if you're doing it regularly, and/or with muddy bikes.
And you do need to remember not to drive the bikes into height restrictors, which are more common than you'd maybe expect.
Tow bar placement is painfully expensive, at just under a grand to fit the tow bar, electrics and holder.
Remember that security is always an issue if you leave the car unattended. People will steal bikes very quickly
Final thought: The Saris Bones 3 will fit the E Class. I'd be wary about using it for a day long journey but it should be fine for short trips. Here's a photo of the Bones 2, but there's also a Bones 3.