I have 3 Sony readers including the T1. I also use calibre (same version/installation) to sideload books to my mother's kindle 3(keyboard)
At present there do not seem to be any problems. As Theducks suggests I do use a plugboard for my Sony(s) and the K3, but not necessary. I can change/delete them and they only affect the reader they apply to.
I am sure you will be awed and amazed by the collection handling capabilities of the Sony when used in conjunction with calibre. All of my books are in author collections with series sorted and displayed clearly within these collections. And they stay sorted (books don't move, collections don't move in the respective screens). Still haven't completely figured out how to do this on the kindle but it must be possible?
As well having an additional reader or two is great, although I may have too many
Helen