The biggest pros are that your actual IP can be hidden from view and your data is encrypted to your ISP. Most consumer VPNs also give you a choice countries/cities where your public IP appears to originate. The biggest con is that the extra hoops your signal jumps through reduces your speed. If you have very good speeds going in, then the reduction is usually not a big concern.
A VPN can't hurt, but a lot depends on how you are connecting to the outside world.
If you are just using the basic WiFi from whatever RV park you are in at the moment, then you are responsible for your own security, Just like using the local coffee shop wifi.
If all you do is watch movies and browse Facebook, maybe you can get away without one.
If you are doing online shopping, online banking, communicating with you medical providers, communicating with any financial organizations, you really should have a VPN and some reliable security applications.
If your anti-virus software is giving you that message I would not trust it. Being in IT for 40 years I tend to keep up to date on the latest developments. In the past the built-in Windows Defender did a poor job of protecting your computer. In 2019 Win 10 Windows Defender became one of the top 3 anti-virus programs. Its is built in and free, and does not slow down your computer. But on public networks you need a VPN also.
What browser you use matters also. My personal favorite is Brave that I have used exclusively for 4 years. It is used mostly by IT professionals and younger computer savvy individuals. It is easy to setup and does not require special attention. It is more secure than other browsers and is the fastest (by far) because it blocks all ads. You may think you are blocking ads until you see all the empty holes on web pages where ads would have appeared. You may think it is a gimmick because it pays crypto rewards but take a look at at. It is no joke.
To answer some questions:
Using the Chrome browser.
Several computers on Windows 7 & 10.
AVG Free & Avast free.
Almost never use public WiFi.
Have cable internet at home and ATT Mobley on the road.
I do access online banking and investments.
Think that’s all.
If you are connecting only through your Mobley and not doing anything frowned upon by the government (file sharing, pirating movies, Kodi, etc.) there is little benefit to operating a VPN for most people. The real danger is when you connect to public wifi networks provided in airports, coffee shops, hotels, even RV parks, etc. as many of these are configured in such a way as to allow 3rd parties to snoop on your data. Most often this requires the 3rd party to be local, but the wifi routers used in such operations are also more subject to hacking.
I have been using Avast for years on my personal machines. They definitely tell you about stuff which is a hook to get you to sign up for the paid version.
If you are a belt and suspenders kind of person go ahead and get a VPN tunnel. If you travel a "lot" and use coffee shop and airport WiFi a lot you might want a VPN.
Another vulnerability is RV and hotel WiFi.
Most (all) financial software has point to point encryption so I don't sweat it much as I don't use public WiFi much. I am also tethered to my cell network most of the time because most public WiFi is crap.
My bottom line is that I don't check any of my financial stuff on airport and coffee shop WiFi.
Are there holes in my plan? Sure. But it's a scary world and you do your best.
The thing about using free security service (in MY poor little mind, at least) is the old line, "You get what you pay for."
But you should know why you are using a security package.
The security software generally sets the settings in Microsoft security suite and lets MS do most of the work. It then monitors MS security looking for things that might get past it.
If you know enough about Windows Security, then by all means set it up and use it. The default is pretty good for most attacks you are likely to encounter, but you really should understand how it works, if you're going to depend on it.
As for a VPN, most of the time you probably don't need one, but then, most of the time, you don't need those airbags in your car, either.
Security is more than just anti-virus software. The operating system itself has vulnerabilities that are constantly patched. Win 7 hasn't been updated since Jan 2020 unless you are paying Microsoft for extended support. I would never use a Win 7 PC for any sensitive or financial data. If you have home sharing/homegroups setup between your Win 7 and 10 PCs they could all be at risk.
I use Express VPN. This VPN allows you to share with all your Multiple Family devices. Desktops, Laptops, Phones, Android TV, Amazon Firestick if you have one connected to your TV. Fast and I do not notice any connection problems of speed. Just another layer of security. Can't hurt. Internet is a big ugly place full of hackers and scammers. Can't apply to ROKU box as they use their own operating system.