Android/iOS is an interesting idea for a business.
They already have secure app distribution. A private channel in the Google play store or via app store adhoc.
Communication between the devices via a server should be possible at least using HTTPS but also private/public key encryption. Doesn't have to be an actual server just one of the devices in server mode.
American Airlines way back had "more room" seats which were only slightly more expensive. I loved it and became loyal. But then they stopped. I guess not a lot of people wanted to pay the few bucks.
They still have those seats; they're branded as "Main Cabin Extra". They're not super expensive, but the price will vary depending on the perceived desirability of the specific seat you select (i.e., an extra-legroom middle seat probably doesn't cost as much as an extra-legroom aisle).
Most airlines also build free or discounted access to those seats into their frequent-flyer perks, though Delta has recently begun cutting back hard on that and treating it as a possible-but-not-guaranteed after-booking "upgrade" even for their top-tier customers.
I work for a password manager that has had teams for a while. We have an encryption key per record with fast search. An open source command line SDK and Java desktop client which is great for linux. A great Android app with autofill, material design UI (more to come), which has been in the Google Play store since day 1, etc.
I'm obviously biased especially about the Android client :) but IMHO great iOS (and SDK), Android, Web Vault, browser plugins, Windows Phone, Surface, etc.
With the watch I don't take out my phone to see what the vibration is for and then most likely getting lost in the phone, surfing etc.