Hi Dave90,
I think theorical value is "good line for Black positional player" (my POV)
I recall first moves (because I am trying to improve my index

): 1.e4 e6 2.d4 d5 3.Nc3 Bb4 4.e5 c5 5.a3 Bxc3+ 6.bxc3 Ne7 7.Qg4 Kf8
This Kf8 move happens in other positions too:
- 1.e4 e6 2.d4 d5 3.Nc3 Bb4 4.e5 Ne7 5.Qg4!? Kf8 (5...c5 can lead to Spassky-Murey line with 6.dxc5 ; 5...Nf5 is line analyzed by Kindermann in the oo-Winawer book ; 5..oo can lead to main lines except for 6.Bg5 Hebden vs E Prie, 1984 ....where I advice the Nd7 move as played in similar position Ivkov-Angos,1960 )
- 1.e4 e6 2.d4 d5 3.Nc3 Bb4 4.e5 Ne7 5.a3 Bxc3+ 6.bxc3 Nc6!? 7.Qg4 Kf8
- 1.e4 e6 2.d4 d5 3.Nc3 Bb4 4.e5 b6 5.Qg4 Kf8
- 1.e4 e6 2.d4 d5 3.Nc3 Bb4 4.e5 c5 5.Qg4 (C17 Russian variation Couso-Berg,Stockholm 2002 (NIC YB 66)) Kf8? ... and here Watson gives the main idea for White: 6.dxc5! Bogoljubow-Fry,SouthSea 1950
With the Kf8 move, Black is playing a slow positional system compared to other main lines (the oo Winawer or Nf5).
It's "defensive" system according to the common idea of economy in defence: king is used alone to defend the g7 weakness. This economy can be used by Black for a queenside counte-attack usually along the c-file.
Not so active Rh8 and some weakness on dark squares are the main disatvantages...but Black feel safe without now square weakness. In the long term plan, Black can seek where to put his king in safe place: going to h7 after h6 move ? going to queenside ? staying on f8 square ?
Here are some variations, 8.Bd2! being the "modern" move and 8.h4 the old one and quoted 8.h4?! in Short's old book about French.
A) 8.Bd2 Qc7 (8...Qa5 9.h4 Qa4 10.Rh3! Videki-Vareille,Toulouse 1995 (McDonald)...hungarian Videki won CEIT tournament this 1995 year ; 8...b6 Apicella-Legky,Saint Quentin en Yvelines 2003 (EE Juin 2003) ) 9.Bd3!? Kristjannsson's idea (9.Rc1 Qa5!? Polgar-Nikolic,Linares 1997) b6 10.Nf3 (10.Nh3 Ba6 Leko-Nikolic,Bastia 2001; or 10...cxd4) Ba6
Interesting game is: Stefansson-Nikolic,Elista 1998 ... and you can work about Nikolic's games in this line
B) 8.h4 Qc7!? Nikolic's novelty in his game vs Kasparov in Horgen 1994 (8...b6 is quieter) 9.Qd1! and now 9...b6 with the common plan (exchange light bishop square with Ba6..and maybe a later h6-Kg8-Kh7)
you can reach same position after 8...b6 9.Qd1 Qc7 ... it can be useful to work both lines with 8...b6 or 8..Qc7
C) 8.a4 Qc7 9.Nf3 b6 Aschenbrenne-Eingorn,Graz 1998 10.Ba3 Ba6 and Djurhuus-Ostenstad,Norway 2004
D) 8.Nf3 Qc7 Sokolov Andrei-Crut,St Chely d'Aubrac 2004 9.Bd2 cxd4 Stefansson-Nikolic,Elista 1998 see A)
E) 8.Bd3 Qc7 9.Bd2 transposes
F) 8.Qd1 Qa5 9.Bd2 Qa4 10.Nf3 b6 11.c4 Ba6 Ziatdinov-Levitt,Dublin 1991 (Psakhis) or 11.Bd3 Ba6 Beliavsky-Nikolic,Tilburg 1993
Nice summary. Some things to add:
After 1.e4 e6 2.d4 d5 3.Nc3 Bb4 4.e5 c5 5.a3 Bxc3+ 6.bxc3 Qc7 white normally plays 7. Qg4 expecting 7.. f5
But 7... Kf8!? is an alternative, confusing white a bit, but often transposing while Ne7 is difficult to avoid.
1.e4 e6 2.d4 d5 3.Nc3 Bb4 4.e5 c5 5.a3 Bxc3+ 6.bxc3 Ne7 7.Qg4 Kf8 8. Bd2 Qe8!?
is interesting, with the idea to go to a4 in another triangle.
After 9. a4 Bd7 10. a5 Bb5 still black exchanges the bishop...