In both Solo and Solo DL, you get s/p/G data (GPS speed, GPS position, and G's) + lap times and predictive lap timing.
Solo DL, in addition, allows you to connect to and download data from the ECU.
For the M3, here are the additional data channels you get using a CAN connection to the ECU. Some of these data channels are extremely valuable, i.e. Gas Pedal Position, Brake Pressure, Steering Wheel Angle, etc.
For example, when braking, brake pressure is a more precise indication of your brake point, so is steering wheel angel for cornering.
Are you spinning your inside wheel coming out of a corner? Just check the individual wheel speed.
Gas Pedal Position
Wheel Speed, LF
Wheel Speed, RF
Wheel Speed, LR
Wheel Speed, RR
Brake Pressure, LF
Brake Pressure, RF
Brake Pressure, LR
Brake Pressure, RR
Engine Coolant Temperature
Manifold Absolute Pressure
OBDII connection on the other hand, only gives you about 9 channels of data.