Yes my W220 Erisin install was comparatively very easy, just more add ons, because that Head Unit was specific to W220 Dash and CAN Bus, and that Car has CAN Bus on Steering Wheel Buttons
The R170 does have at least 1 CAN for Powertrain, but I'm not 100% whether it has a Body CAN as well, or if H/U will talk to the protocols that are used on R170 ....................
I have no Steering Wheel Controls on the standard R170 Steering Wheel, but have a C Class W203 Steering Wheel with Buttons, that will fit the Car. Need to do a ton of searching WIS Wiring Diagrams for CAN Bus on both the R170 and W203 Cars and then probably have to build a Steering Angle Sensor / Clockspring Squib out of parts from both cars, to get extra wire cores, then get a W203 Steering Column Module, plus chopped wiring with correct plugs, then finally hope and pray the CAN Protocols are the same between the 2 Cars
The Steering Wheel I bought was also available with Paddle Shifters, so I may decide to add those as well at the same time
TBH I can't see MB re writing all their older CAN Protocols as models progressed, which gives me hope that I'll eventually get it all running on CAN bus
I just don't have a whole spare time day to trawl all the wiring diagrams right now
So atm, all Head Unit Functions are hard wired via the "SWC etc" Harness supplied with the H/U, but yeah, the H/U has a CAN Decoder built in and designed to work with C Class W203
Fingers are well and truly crossed