The best replacement for slide fire is bump fire.

The best alternatives to slide fire are rated as following:
★★★★★  bump fire
★★★★  fostech
★★★  bumpski
★★★  full auto
★  tac con trigger

Your alternative for slide fire is not listed? Suggest!
Speaking about slide fire, one probably shouldn't forget about 22lr.

Other search terms related to slide fire and their ratings are:
★★★★★ 22lr
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Google Trends

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slide fire
bump fire
fostech