According to Mr. Ronald (Ron) Denny Klinger, a bridge expert, prolific author of bridge publications, and theoretician of the highest caliber, the concept behind the Extended Stayman conventional method has some drawbacks, which are quoted below. Blog.

Justification for Variation

	1.	It gives a lot of information to the opponents. While finding your best contract is your primary aim and may entail revealing part of your hand pattern, it is usually best to give the opponents as little information as possible.
	2.	Since the reply of the opener can be at the three level, you cannot safely use the 2 response to bail out of 1 No Trump with a weak hand.
	3.	Neither simple nor Extended Stayman provides a satisfactory solution to the problem of responder holding invitational values with 5-4 in the Major suits. You cannot afford to transfer to the 5-card Major and then bid the other Major. That is played as game-forcing.

Variation of Extended Stayman

After reviewing and studying the fundamental concept for the conventional method designated as Extended Stayman, Mr. Ronald Denny Klinger concluded that the identical concept could also be applied and employed if the opening bid was a suit bid and the rebid is 1 No Trump, as in the following bidding sequences. However, the continuances are not identical as shown below.

Opener		Responder				Opener		Responder
1		1		or		1		1
1 NT						1 NT

The opener may or may not have a 4-card Major suit. There are some approaches or bidding systems, which allow for a 1 first response by partner on holdings containing a 4-card Major suit and permit, if not strongly recommended, a 1 No Trump rebid by the opener on holdings containing a 4-card Major suit. Bridge players employing the Walsh bidding system do allow this possibility and encounter this bidding situation and who, as a consequence, must have a means of finding a possible fit in either or even both Major suits.

Although originally not designed for a suit and then a No Trump rebid bidding sequence, the continuances of the original Extended Stayman concept, according to Mr. Ron Klinger, apply suitably and appropriately also for this particular bidding sequence, although they are not identical.

The following responses are not identical to those of the Extended Stayman conventional method. They have been developed by Mr. Ronald (Ron) Denny Klinger of Australia for employment after opening a suit on the one level, generally without competition, and a rebid of 1 No Trump. These continuances are as follows and are designated also as Extended Stayman responses. The bridge player must note the distinction between the two situations.

Opener		Responder		Meaning
1		1
1 NT				The opener may or may not have a 4-card Major suit. This approach is partnership agreement dependent.
		2		This continuance may not be necessary unless the partnership agreement is to allow a natural 1 first response on holdings containing a 4-card Major suit. In this case, this bid becomes Extended Stayman asking whether opener has a 4-card Major suit.
Extended Stayman Continuances
2				Shows minimum values and no 4-card Major suit.
2				Shows minimum values and a 4-card Heart suit. Denies a 4-card Spade suit.
2				Shows minimum values and a 4-card Spade suit. Denies a 4-card Heart suit.
2 NT				Shows minimum values and promises both 4-card Major suits. Compare original Extended Stayman.
3				Shows maximum values and promises both 4-card Major suits. Compare original Extended Stayman.
3				Shows maximum values and no 4-card Major suit.
3				Shows maximum values and a 4-card Heart suit. Denies a 4-card Spade suit.
3				Shows maximum values and a 4-card Spade suit. Denies a 4-card Heart suit.

The following example should clarify this concept, which is first initiated once the No Trump bidder has denied holding a 4-card Major suit after bidding 1 No Trump.

Opener		Responder		Meaning
AQJ4 K75 983 KJ103		K986 Q10 AQ76 A97
1
		1
1 NT				The partnership agreement is to first show a certain value-range, an approach which by-passes a 4-card Major suit.
		2		With this bid the responder triggers the Klinger Extended Stayman conventional method to discover whether partner has by-passed a 4-card Major suit. (Note: this bid is not game-forcing.)
3				With a 4-card suit in Spades the partner shows that he does indeed possess a 4-card suit in Spades. If the opener had 4-cards in both Major suits, then the opener would bid first the lower-ranking Heart suit. The jump shows maximum values.
		4		After discovering that the partner holds a 3-card suit in Spades, the responder, with game values, bids game in Spades knowing that there is a 4-4 fit.

Once the opener has clarified and more closely defined the holding via the continuances designated by Mr. Ron Klinger as Extended Stayman after the rebid of 1 No Trump, then the responder is better qualified to judge and establish the final contract. The possibility of agreeing upon a Moysian fit, or a 7 card trump suit, is more frequent. Source: Taigabridge by Mr. Gordon Bower.

If you wish to include this feature, or any other feature, of the game of bridge in your partnership agreement, then please make certain that the concept is understood by both partners. Be aware whether or not the feature is alertable or not and whether an announcement should or must be made. Check with the governing body and/or the bridge district and/or the bridge unit prior to the game to establish the guidelines applied. Please include the particular feature on your convention card in order that your opponents are also aware of this feature during the bidding process, since this information must be made known to them according to the Laws of Duplicate Contract Bridge. We do not always include the procedure regarding Alerts and/or Announcements, since these regulations are changed and revised during time by the governing body. It is our intention only to present the information as concisely and as accurately as possible.