Taken all in all, neither the Klesteritzky Gambit nor the Allgaier Gambit seems wholly satisfactory. It appears, therefore, advisable to put off 4 (]P-KR4, which though shaking the mass of Black Pawns endangers White's King side too much.
A later opportunity may arise for that advance. From this point of view arise the Gambits bearing the names of Salvio, Muzio, and Philidor.
1 P-K4
P-K4
2 P-KB4
PxP
3 Kt-KB3
P-KKt4
4 B-B4 ...
The defence of Philidor is
4 ... B-Kt2
5 P-KR4
P-KR3
6 P-Q4
P-Q3
7 P-B3
Kt-QB3
Black attempts to maintain his Pawn plus and makes it hard for White to shake the Black Pawn mass.
8 O-O
Q-B3
In order to continue with KX-K2. White is now forced to essay hazardous onslaughts.
9 P-KKt3?
B-R6
or
9 P-K5?
PxKP
10 PxBP
Q-Kt3
[!!w1]
[!!w1]
Another line of play.
7 Kt-B3
Kt-QB3
Now 8 ..., P-X5 threatens the QP
8 Kt-K2
Q-B3
White's attack is not convincing. The Russian master Tschigorin, one of the greatest connoisseurs of Gambits, made use of the KXP, not of the KRP, in order to break the chain of Black Pawns.
5 O-O
P-Q3
6 P-Q4
Kt-QB3
7 P-B3
P-KR3
8 P-KKt3
P-Kt5
9 Kt-R4
P-B6
White has here the opportunity of a large number of attacks without having to resort to the sacrifice of a piece. If 10 X-Q2
Black can hardly reply ... KX-K2 on account of 11 [!)QXxP and will therefore have to develop the X to B3. The position is difficult for either side.
Black may attempt to meet Tschigorin's plan by an endeavour to Castle early.
5 O-O
P-Q3
6 P-Q4
P-KR3
7 P-B3
Kt-K2
8 P-KKt3
P-Kt5
9 Kt-R4
P-B6
But then
10 P-KR3
P-KR4
11 B-Kt5 ...
and the position is rather unbalanced. The White QB is too powerful.
All in all, Tschigorin's line of play seems to be appropriate and far more convincing than any other.