If you're located in USA, then it's recommended to install the latest firmware version as it always fixes some bugs or adds some new features.
However, before you do that, please pay attention to the release note. For example, the latest firmware for Touch P5 indicates that the router will reset after the upgrade, which means that you will lost your current configuration on the router. In this case, it's recommended to export your current settings before the upgrade, and then restore these settings after the upgrade due to the firmware upgrade guidance file.
Any other problems, just don't hesitate to post here.

Thank you for the quick response. I also posed the same question to the TP-Link US support site via email. I'm sure they are likely to mirror your suggestion and I will export and then import my settings from the Ethernet connected PC.

Meanwhile I have a question about router security in general and did nor see a forum subject area to address such a question, so I'll ask it here.

I'm using the default WPA2 to encrypt the passkey of this router. However, the router has a default 8 digit pin to go with the 2.4GHz and 5GHz radio SSIDs. Since the default SSID names and PIN passkey are public knowledge what difference does encryption make to keep unwanted connections from happening. It would seem prudent to me; at a minimum, to change the pin number to something different, of different length and including letters and other allowed characters. What do other people do to help avoid unwanted connections and piggy backing.

Also, the router uses a default, publicly known IP address assignment. Do other router owners with security concerns change this IP setting and if so how is that done?

Just don't worry about that.
Actually PIN code is consist of 8 numbers due to the WPS standard (Wi-Fi Protected Setup), which aims to simplify the wifi connect process. And the PIN code is changeable, you can login the admin page of Touch P5, refer to Advanced -> Wireless -> WPS, click Generate to change the default PIN code so that other people will not be able to connect to you with the default one.
The WPS provides two kinds of simple wifi connections, by manually typing in the PIN code of the router on the client or pushing the WPS button together both on the router and the client.

Without WPS, customer needs to manually find and connect to a wifi, and type in the wifi password before successfully setup which seems a little painful especially for some customers with lots devices.
WPS is designed to solve that and it uses the PIN code to recognize each other, when connecting, it also uses the WPA2 encryption which is very secure. You can search google for more details about WPS.

If you do concerned about that and don't want any others to connect to the router through this method, you can disable PIN and WPS of the router on the admin page.
Disable PIN: Advanced -> WIreless -> WPS -> Router's PIN
Disable WPS: Advanced -> System Tools -> System Parameters -> WPS

OK,now I understand. I have WPS enabled and generated a new 8-digit pin number. This will effectively keep any neighbors from connecting to my broadcast SSID using the default PIN. The 9 WiFi items I use on my internal network still connect fine. If I add a tenth WiFi item I'll need to use the newly generated PIN to make that connection.

Thank you

The quote below is what the tech support folks responded with, which is rather vague since they do not indicate which bugs were fixed. I think I'll forgo the firmware update unless something seems broken.

"Thank you for your question. You can update to the firmware listed although since it is a bug fix firmware, unless you are experiencing the bug, I would not recommend doing the upgrade. Please let me know if you are experiencing any bugs or problems with the router so I can assist you with addressing them."