[kgr]

We now play that 4m is RKC if the fit in m is confirmed before.
We also play short Club (2+) openings. We open 5=5=4=2.
Sometimes it is confusing if 4C is RKC or not, we have less issues with 4D because then it is more clear that both partners have 4+D.
Not wanting to go for complete Kickback yet (fearing 4H confusions).

Do you think it is an improvement to also use 4D RKC when we have a C-fit (this 4D can then even be used if the C-fit is not clearly established). Or am I overseeing other issues?

[blackshoe]

In Bid to Win, Play for Pleasure (1985) George Rosenkranz opined that Kickback is "not that useful" in Romex. Later (the books were published several years apart) his characters are using it as a matter of course, without any mention of this original point. But there are many auctions in which some other agreement than Kickback as to ace asking applies. For example, if someone starts a relay sequence, generally the first relay asks for shape, and the second asks for keycards. There are also auctions in which one player or the other cannot use any BW at all (typically when controls are already known).

Romex usually has clear rules about when things do and do not apply, but I don't remember them all for ace asking bids. I'll have to do some research.

[CSGibson]

I like kickback, especially for minor suit contracts - in fact, we just play redwood, not pure kickback, in my main partnership. I suppose its playable as diamondwood, too. The one issue you have in transitioning from minorwood to a diamond keycard ask for clubs is that when you get a 4♠ response, you have to decide whether 4N is an offer to play, or a Q ask. Personally, in that one circumstance, I prefer a Q ask. Obviously in minorwood you have the room for both an offer to play and a Q ask because of the extra step.

On the other hand, I think the ability to be more nuanced in the auction - being able to suggest slam with 4♣ without asking for keycards or cue-bidding immediately, and having partner still be able to ask for keycards with an appropriate hand type more than makes up for any loss of a natural 4N in one specific sequence.

[RSClyde]

We play 4♦ as RKC for clubs and it is almost never ambiguous. For diamonds it's harder because 4♥ can be an offer to play, so we generally play 4♦ as RKC for diamonds as well but it depends on the auction.

[Zelandakh]

If you agree clubs at the 3 level, play 4♦ as RKCB and 4♣ for other slam tries (cue bidding if agreed but there are other options too). If your club agreement at the 3 level also showed slam interest, an interesting option is to use 3♦ Frivolous. That is not a good idea if the 3♣ agreement was simply GF though, so it requires a good understanding.

If you agree diamonds at the 3 level, play 4♣ as creating a cue auction (with 4♦ being a club cue) and 4♦ as a key card ask. Whether to play the ask as conditional or not is another thing to agree but without Kickback non-conditional is probably best. Again, an option on auctions where 3♦ guaranteed slam interest is a Frivolous 3♥ bid.