And your #1 choice is "Zengo"? To start, cellphones are terrible for privacy, but worse than that, the website is filled with buzzwords that are typical for BS-sellers that try to convince gullible people. I wouldn't trust them with my funds!
If you want privacy, use Bitcoin Core with Coin Control through Tor. To add security, set it up as watch-only online wallet, and sign offline.
There's no need to trust or even pay third parties for this.