For me the flavoured whiskies tend towards being a bit sweet and syrupy, so to drink either as a small aperitif or a with a mixer.

Jim Beam used to do their Black Cherry at full strength and that was a pleasant drink over ice, but they've since dropped it to the 32.5-35% range and it's like the rest.

Blackberry sounds an interesting one to try, but I think getting it for free as you did is the best way to carry out the experiment.