https://www.techradar.com/reviews/invizbox-2-vpn-router
Whenever you add a second router to an existing router, no matter what Invizbox claims this will introduce issues with your basic home network infrastructure. You're still going to make a conscious choice on what works out best. You can't just keep adding more and more routers creating added WiFi networks.
-- Install this 'WiFiAnalyzer (open-source)' app on your P10:
https://play.google.com/store/apps/details?id=com.vrem.wifianalyzer&hl=en_US
Use it to build a heat map of the WiFi coverage range for your primary router and the Invizbox VPN router. Walk through your household and get some actual signal strength numbers close both routers and further away in different rooms, and for both 2.4Ghz and 5 Ghz band networks.
-- Get some numbers on bandwidth speed too, for wired (Ethernet) and wireless (WiFi) and also for both routers. And do your tests when no one is using online access in your household as that can skew any speed tests. Using a web browser, go to
https://fast.com
and use the 'Show more info' button for expanded details. Note the Download, the Upload, and the Latency (loaded) results.
-- You should end up with a relatively sizable database of data, your situation has potentially five different items (one wired for both routers, and two wireless for both). The Ethernet bandwidth is more of a baseline number since that's what feeds the WiFi in your routers so focus on the 2.4Ghz and 5Ghz numbers emitted by your two routers. That's the numbers to use to determine what WiFi networks you want to use for your mobile devices, factoring in what parts of your household are optimal. If it's a matter where your primary router provides better coverage range, take that into consideration.
But if you do want
everything to connect within the oversight of your VPN, you need to intentionally change all your devices (computers, mobile devices, etc,) to use your Invizbox router as your home network gateway. In your phone, delete the WiFi network entry for your primary router so it's always using the 2.4Ghz or 5Ghz band WiFi from your Invizbox.
Lots of useful tips and info here on router placement:
https://www.techradar.com/reviews/invizbox-2-vpn-router
and basic info on 2.4Ghz and 5Ghz band:
https://www.centurylink.com/home/help/internet/wireless/which-frequency-should-you-use.html
A lot of people mistakenly tout just use 5Ghz band since it can provide faster bandwidth but that's a very conditional matter. Depending on the situation, if you're in a spot in your home where you have a strong 2.4Ghz signal (which has longer range and penetrates walls better) but a weak 5Ghz signal, use the 2.4Ghz connection instead. But that goes back to just having some actual numbers to compare so do those coverage and speed tests.