

Yes, this is good, however lockdown mode does NOT protect you against forensic extraction of your data, for example from the Cellebrite tool. Your phone has two states, BFU and AFU (before/after first unlock). To maximize your protection against your data being extracted, your phone needs to have not had its first unlock after being powered up. Lockdown mode does nothing here.
So, use lockdown in general if you like, however, when going through customs or in a place where your phone may be confiscated, power it down fully. Don’t unlock it if you power it up, and don’t use biometric fingerprint or face unlock so you’re not forced to unlock it.
This, 100%. Lockdown mode is a false sense of safety in all honesty. As MegaUltraChicken (he is legend) is saying, you need to have your phone in a Before First Unlock (BFU) state to have maximum protection of your data (and is also phone model dependent)
Here’s a great link to read more about this and find where your phone falls susceptibility wise.