SFP is optional on 737-800 and it is standard on the 737-900ER -- The MAX versions all are SFP aircraft
Ryanair have had the package fitted on their new deliveries in the past year or so which includes a variety of aerodynamic and system changes.
The SFP is a combination package - the two-position tailskid that allows safe use of higher angles of attack and rotation, while others include sealed slats for all take-off flap positions to 25º which allows the airplane to climb up and away more rapidly on shorter runways and increased flight spoiler deflection on the ground to close to that of the ground spoilers, which deflect to 60º. Winglet credit given for lower landing speeds. A reduced idle thrust transition delay between approach- and ground-idle speeds, which improves stopping distances and increases field-length-limited landing weights. A reduction in the camber, or “splay” of the main landing gear by just over 1°, which increases the uniformity of braking across all four brakes and will help tyre [wear] issues.
- some software changes - which allows for around 3700 kgs extra weight for dispatch landing calculations plus lower landing speeds, and around 1700 kgs extra weight (payload) for take offs