I've had a dash cam on all my cars for at least the past 10 years; wouldn't be without one
Thought occurs to me: you ought to try the Tesla Dash Cam before deciding not to have an add-on / assuming it is fine.
Compared to no Dash Cam its great of course - in-built, just plug in a USB stick etc. But an add-on is not the same beast.
Sentry Mode uses a lot of juice. Add-on DashCam will be trivial in that regard.
The side cameras are great to collar someone who keyed your car ...
I find the quality not great. I had a big truck chuck up a stone and crack my windscreen. The dash cam footage, examined frame by frame, didn't show it.
(Possible tip on that, when you press "Keep that clip" button a fair chunk of footage is stored. If safe to do so might be worth stopping immediately after such an event, as that will make it easier to "find" the exact moment).
Unless it has changed? there are also gaps in the footage - between sections. That can cause it to miss a vital snippet.
But the surround cameras can be handy ... I have footage from France of a driver coming up behind me at speed on Autobahn (all lanes in use) and then using a slip road for a nearside overtake ... combining rear, side and front cameras