IDPA prohibits the APEX FSS in all pistol divisions basically by prohibiting non-stock trigger position, but allows the internal kits that cannot be seen and do not remove internal safeties. (Magazine disconnects are specifically named as NOT being safeties.)
Look in section 8, Equipment.
SSP: 8.2.1.4.1
ESP: 8.2.2.2.11
CDP: 8.2.3.2.11
http://members.idpa.com/Content/Rules/g0hunysc.eoc.pdf
Are you looking at the old rules or the new ones? I just looked at my PDF (no printed book for the new rules) and I see:
8.3.2.2.
2. ESP PERMITTED Features and Modifications (Inclusive list):
• Sights may be changed to another notch and post type.
• Grips may be changed provided they do not weigh more than 2.00 oz/56.7 grams more than the
factory standard weight for that model.
• Robar-style grip reduction.
• Action work may be used to enhance trigger pull as long as safety is maintained.
• Reliability work.
• Aftermarket extractors and pins may be used.
• Internal accuracy work.
• Replacement of barrel with one of factory configuration in a stock or non-stock caliber.
• Plastic plugs may be used to fill the opening behind the magazine well.
•
Aftermarket triggers and trigger work that result in the trigger being forward or rearward from the
stock trigger position.
• Externally visible trigger over travel stops.
• Hammer and other trigger action parts to enhance trigger pull.
• Checkering, serrating, and stippling.
• Reshape trigger guard.
• Extended and/or ambidextrous thumb safety.
• Extended beavertail grip safety.
• Extended magazine release (button may not be oversize in diameter or protrude more than .2" out
from the frame).
• Ambidextrous or right side magazine releases.
• Extended, trimmed, and/or ambidextrous slide releases.
• Heavy or cone style barrels on firearms with barrel lengths of 4.25" or less.
• Recoil spring guide rods and dual spring recoil systems made of material that is no heavier than
stainless steel.
• Slide inserts to accommodate a different recoil assembly design.
• Modification of the magazine well and add-on well extensions.
• Custom finishes and engraving may be applied.
• Aftermarket slide cover plates.
• Slides with front cocking serrations, tri-top, carry melts, and high power cuts.
• The use of grip tang extensions.
3. ESP EXCLUDED Features and Modifications (NON-Inclusive list):
• Steel dust covers and rails over 3.25" (as measured from the rear of the slide stop pin to the most
forward portion of the dust cover or rail) are not permitted.
• Removal of material from the exterior of the slide other than front cocking serrations, tri-top, engraving, carry melts, and high power cuts.
• Oversize diameter magazine release buttons.
• Trigger shoes.
• Disabling the slide stop.
• Swenson style thumb shields and frame mounted thumb shields.
I put the whole section in for reference.
The Apex trigger would be prohibited under SSP because of the
externally visual modifications other than listed in the Permitted Modification section. clause.