I don't travel often, but this looks like a good option to have... although I don't really do any finicky stuff with machines/phones/etc that I use regularly. if I were using a RPI3 as a phone then I'd 100% do something like this (hope you understand the analogy).
almost everyone i know, even the staunchest pro-privacy types, are not willing to go toe to toe with a US customs and border agent over phone unlocking. they just aren't principled enough. i don't blame them.
worse, there's no telling what malware goes /in/ to your phone if it gets imaged. yeah yeah, call me a conspiracy nutter, i don't care after what snowden showed us. if one of their machines touches my unlocked phone, i'd consider it compromised.
so, naturally, i have a second phone. this offers many benefits:
- no potential mission critical disasters if i lose it via robbery, water, or power tripping US border patrol agents e.g. forgot to backup some particular important message or whatever
- keybase paper key lets me keep in touch with people i need to, provision new devices if need be, and means i can burn the keybase app upon re-entry into US as it's not something like SMS that they are cognizant of
- using whatsapp on foreign SIM gives me some cred as far as not having a purely empty phone, some human interaction, etc. yeah they'd get dragnetted but it's a smaller set of people than my main phone
- if it gets imaged by border agents, i can trade it in for a new one at some point in the future or just recycle via apple recycle program. no big deal.
^ ...which are mostly money-making scams anyway, targeting fat corporate and university budgets in return for limited benefit. Rarely do you learn anything that you couldn't otherwise learn from published materials a few days later.