Does the the 9150 RD allow the use of smaller gears than the 9070??
I currently have a 9070 group… but want to use a 32 on occasion.
Another question… I assume the 9150 RD is fully compatible with the 9070 group I have now.
32 could be a real stretch, dependent of RD hanger and dropouts geometry.
If you want to be sure using 32 tooth cog, get the Ultegra 8050 GS RD.
Other than this, no problem to use either of the derailleurs with any other e-tube Di2 parts.