IDPA:
The Glock extended mag release for small frame Gen 3 Glocks (1981) is the
standard part on the Gen 3 G34/35.
The Glock extended mag release for small frame Gen 4 Glocks (8794) is the
standard part on the Gen 4 G34/35.
Therefore, according to rule 8.2.1.2-C,when these parts are installed on other
small frame Glocks, e.g. G17, they remain legal in SSP.
https://www.brownells.com/handgun-parts/frame-parts/magazine-release-parts/magazine-releases/extended-magazine-release-prod22998.aspx
https://www.brownells.com/handgun-parts/frame-parts/magazine-release-parts/magazine-releases/magazine-catch-reversible-extended-0-75-fits-gen4-sku100700094-69854-150579.aspx?sku=100-700-094
The same applies to Glock extended slide stops:
https://www.brownells.com/handgun-parts/frame-parts/slide-catch-parts/slide-catches/extended-slide-stop-levers-prod23432.aspx
However, if you install 3rd-party mag release and/or slide stop, then the gun
would be bumped into ESP.
"IDPA 8.2.1.2 - SSP Permitted Modifications (Inclusive list):
C. Magazine releases, slide stops, safety levers, de-cocking levers, hammers,
and triggers, that are stock on one SSP legal firearm may be used on another
SSP legal firearm from the same manufacturer provided they are drop in
replacements. Parts in this list must come factory installed on standard
production firearms. Special parts that are available installed only from a
factory custom shop are not eligible in SSP."
USPSA:
USPSA had a similar rule as IDPA for the Production and Carry Optics divisions.
However, effective in 2018, Production and Carry Optics guns may replace
factory mag releases and other small parts with factory or 3rd-party parts and
remain legal in those divisions.
These are the 3rd-party parts I prefer:
https://www.brownells.com/handgun-parts/frame-parts/magazine-release-parts/magazine-releases/vickers-glock-extended-magazine-release-prod25364.aspx?sku=100-700-094&avs%7cManufacturer_1=tangodown
https://www.brownells.com/handgun-parts/frame-parts/slide-catch-parts/slide-catches/enhanced-slide-stop-for-glock--prod42969.aspx
"Appendix D4
21.6 Exchange of minor External components Sights, firing pins, firing pin
retainers, pins, extractors, magazine releases, slide stops, thumb safeties,
triggers, hammers, bushings, and ejectors MAY be replaced with OFM or
aftermarket parts.”
