Whether or not I chose a CI pan would depend on the finish I sought. If seeking a tightly seared exterior, rare or fairly rare interior I might well go with a pan. In that case the pan should be quite hot and the steak(s) should be seared in a little oil. The process is pretty quick. Sugar should not be in the seasoning as the heat is too high for it. If going for a grilled-flavor finish (or if I didn't want to deal with a pan), with a med-rare finish, I'd grill.
The seasoning you link to is better suited to grilling.
For a coffee-cocoa thing that's fairly simple you could go with a mix of equal parts finely ground coffee, bittersweet or unsweetened cocoa, a ground chile, ground black pepper, and a half-part each of granulated garlic and onion. If using the grill add a pinch or two of sugar if you wish.
Dry the meat, salt rather lightly on all sides, wait a few minutes, then apply the rub lightly on all sides. Finish with another light salt application.
If using a pan - and if desired - you can lightly sprinkle a little sugar on the seared side of the steak after it's been seared.
If you go a different rub route the same applies: avoid much sugar, if any, in the rub if using a pan; add a pinch after searing, if you'd like.
[Imo, the 'true' taste of beef needs help. I know many disagree. Unseasoned or salt only, or the like - well, one bite and then the dog can have the rest. Too lacking to me.]