Battery Isolator vs Engine Kill Switch

I'm building a kitcar electrical system from scratch and am not sure if I want a battery isolator or an engine kill switch (which will ground alternator in addition to disconnecting the battery).

This will be mostly a road track, with a little trackday use. Is it useful to have a driver-accessible kill switch or is it still safe to use the tried and tested method of simply turning off the ignition on a road car (I have one of those aircraft-style ignition switches you can quickly flip off). It's not clear to me if the kill switches became popular purely because of racing mandates (for track marshals to be able to kill engine). My main argument against the kill switch is that it adds another potential failure point to the electrical system. I understand that simply turning off the ignition leaves the battery connected.

Either way, I do want some way to disconnect the battery when the car is in storage. So if not a kill switch, then with a simple 2-pole isolator. In this case, I would like to isolate the negative side of the battery.

Thanks for any feedback on your experiences with these devices!

I use both, and all of the race cars that I wire will have both. The ability to stop engine without having to fully power down the car is almost a requirement nowadays.

Both, and I'd put the isolator in an area that whichever sanctioning body you're running with likes.