Especially the transients are a problem. IIRC certified-for-automotive parts have to endure >100V input, which e.g. may happen when the battery connection is flaky and the engine is running, due to the sudden load drop.

What's missing on this setup imho is a) a solid power connection (those 12V sockets are known for being loose because of wildly varying manufactoring tolerance) and b) the lack of a supercap+diode setup to prevent brownouts during engine start.

The vast majority of aftermarket electronics won't survive a load-dump transient. This includes every AC inverter, every USB charger, every laptop PSU, whatever you find at the store.

Most 12v-targeted electronics are good to about 30v transients. The DC-DC converters would likely be no more or less susceptible than the DC-AC inverter used here. Just quieter, smaller, and more efficient.