Improve your GMing: Battle of Wills

Rating: 3 of 5 stars the first time used; 4 thereafter

Details: The Battle of Wills is Justin Evans generic adaptation of the Duel of Wits mechanic in Luke Crane's Burning Wheel. It is a system to resolve social conflicts. The rules and free printable cards can be found on SinisterGame.
The quality/layout of the cards and of all other SinisterGame products (all free) is excellent.

Usage in the session: The characters needed to require an object from a white dragon. They could have waged combat but they tried to bargain for it (as hoped). Instead of running a skill challenged I decided to give the Battle of Wills a try.
We varied the rules given on SinisterGame a bit. I, as the GM, always chose my card first. Then did the party agree upon their strategy and upon a speaker who would make the skill check. They could choose either to just play a card or to do some roleplaying. If the went with the roleplaying I decided how good the arguments were and rewarded a bonus to the speakers skill check.
The other characters had the opportunity to do other things while the speaker brought forth his point. Maybe trying to determine how much the object was worth to the dragon or something similar. But they passed.

Impact on our session: The system appealed to both, to the players who like roleplaying and to the strategists who discussed which skill to choose and who kept track of the cards already played in order to keep the chances of an automatic defeat low.
The drawback of using the system and the only reason why I did not give a rating of 4 stars is that the game flow had to be interrupted in order to explain the rules. The atmosphere did suffer a bit because of that.
But my players did enjoy the Battle of Wills and liked it better than a skill challenged. Reason enough for me to use the Battle of Wills again.

Advice: I went along with only three skills to choose from ('Intimidate', 'Bluff', and 'Diplomacy'), which all were based on charisma. Which was later criticized by a player since as a result only two characters became speakers for the group. It would have been better if I had chosen from a broader variety of skills, for example Insight (which is based on Wisdom) for 'Slippery Slop'.
Another things I still ponder on is whether I should give a automatic point if due to the combination of cards a player has an automatic defend. I do like the idea to grant a success if the card combination came up because of pure luck and not due to conscious decisions.
But if in such a situation a check is done, the chance of failure should be smaller than that of the opposed check that otherwise would have taken place. Maybe the opponents skill modifier associated with the card he did select would make a good DC.