The option "Preview Only Changes" is very usefull for large amounts of data ( i use it on 15000 files and 400 folders). When using this over LAN/WLAN you will see first the whole tree in source and destination and little by little the folders will be removed, if they are identical. Only the things to sync will remain in the both trees.
This process takes a long time (nearly 3 hours). The functionality in general works fine, but it would be nice to see the status of syncing (in process or finished).
Problem is : while waiting on the finished preview you see the source and destination tree with a lot of folders. To decide if you want to sync or not while preview you have to click on the folder to see the changes. But when the folders aren't processed by toucan they are empty (normaly you can see this be the + in front of the folder). So you have to click a lot of folders with subfolders yust to see, that toucan hasn't finished previewing yet.
I used following otions:
function - equalise
file checks : file size, modification time
other : retain timestamps, retain attributes, ignore read-only, preview only changes