What is the best alternative to SP Camera on iPhone?

Discreet - Black screen camera, S tier, #1 in discreet recording.

Is there a free alternative to SP Camera?

Yes: Discreet - Black screen camera (S tier, #1) is free to download, with in-app purchases.

Yes. 1 app ranks above it in discreet recording: Discreet - Black screen camera (#1).

SP Camera is A tier, #2 of the 6 tiered apps in discreet recording. Here is everything that competes with it on iPhone, in tier order.

1
Discreet - Black screen cameraShigher tier
Free + IAP · ★ 4.4 · 6,948 ratings · score 89
Camera app that takes photos and videos with a black screen so the shooter does not draw attention.
3
InviCam: Black Screen CameraA
Free + IAP · ★ 4.2 · 1,492 ratings · score 82
Records video and photos with the screen turned off, with an encrypted album locked by Face ID or Touch ID.
4
Black Screen CameraB
Free download · ★ 3.8 · 8 ratings · score 77
Records video with an always-visible orange REC banner and a Stop button shown over the screen while recording.
5
Secret video recorder - NoCamB
Free + IAP · ★ 4.4 · 5,867 ratings · score 74
Takes photos and records videos on a fully black screen, so the capture is not visible on screen.
6
Secret Recorder (Black Screen)C
Free + IAP · ★ 2.4 · 14 ratings · score 65
Dual-camera video recorder that dims the screen to black while recording and keeps recordings on the device.

What is the best alternative to SP Camera on iPhone?: Discreet - Black screen camera, S tier, #1 in discreet recording.
Is there a free alternative to SP Camera?: Yes: Discreet - Black screen camera (S tier, #1) is free to download, with in-app purchases.
Does anything rank above SP Camera?: Yes. 1 app ranks above it in discreet recording: Discreet - Black screen camera (#1).