The main difference lies in Mercedes-Benz, VW, Audi software and adapters to work with.
Auro OtoSys IM600 price is: 3450USD/unit with free shipping.
Software difference:
Auro IM600 canread PIN/CS from AUDI Q5/A4/A5 2015-2017 and learn keys to Mercedes-Benz, but IM100 cannot work with Mercedes-Benz, VW, Audi for immobilizer functions.
Adapter difference:
IM600 use UP400. IM100 use UP200.
Up200 doesn’t allow for eeprom and use of breakout leads through the custom pinouts.
Edit to update: Key Programming Tool IM100 is confirmed to have luck with Mercedes-Benz immo.
Now Otosys IM100 with UP400 can work for Mercedes key programming as well as Otosys IM600 does.
Immobilizer functions: OtoSys IM100 vs IM600:
Note: 
This function is supported.
This function is not supported.
Special Declaration:
Some of the listed functions are manufacture dependent. The functions and vehicle coverage expand with new update release.
