Yeah, good idea, some day I would do a post on the blog with info on scoring.
Diversity is fun works in such way: you need to buy a squad built of different units at the very beginning of the level and finish the mission with this squad, so buying it in the middle of a mission will not work.
Thanks for your quick answer.
May I then suggest that you modify the wording of the achievement description to:
"Complete a mission with a squad composed of 6 different units bought at the beginning the mission without losing any."
The only achievements I've still to get are a few directness and squad assault medals. However, it's really very difficult sometimes to appreciate the margin the game gives us to get the directness medals. I'm ranked 80th or so on the Steam Global Leaderboard, so I have a good grasp of the game. Maybe you could consider indicating a maximum ETA to get the Directness medal for a given mission, and maybe a minimum kill % for the ruthlessness medal and maximum $ loss for the efficiency one (for instance, when playing Tokyo Raid in the timed sections, it's impossible to kill everything with the squad, but how many towers can I let live and not kill with bombs?). In other words, I think you should consider giving the player a bit more information to make good tactical decisions. The pathfinder screen would be a good place to display those pieces of information IMHO.
I'm looking forward to hearing from you.