I did so accidentally, and found that it is just way to buggy.
And its UI is also really different, and so it takes a fair amount of time to customize it.
Also, one of the sub versions of 10.5x doesn't read your bookmark file, and then replaces it with 0 entries.
It was a bad move to name it 10.5, since it is to dramatically different from earlier releases. Opera Software should have named it V11, or given it a different number system, to emphasize how different it is from before.