@Rick.E  I'm talking about the M9 Plus that shows Ver:2.8 on the sticker at the bottom of the unit.  That's what would NOT update for me through the app OR show me connected clients.  When I located an M9 Plus showing Ver: 1.2, it updated correctly.  My Main M9 Plus shows (in the app) as Firmware 1.4.3 Build 20200918 Rel. 75286 and working correctly.   My M5's show Firmware Version as 1.5.1 Build 20201022 Rel. 66804.  So, my question relates to the Ver: on the bottom sticker.  IF I locate a new set of M9's with Ver:2.8 on the sticker, will that work correctly from an update perspective and with visibility in to connected client list.  The one I tested last week did not.  Thank You.

@Rick.E 

I bought 3 pack Deco M9 Plus from Costco, online and it was delivered on July 2, 2021. On the bottom of each unit it was mentioned " us version 2.8".

I think that is hardware version.

I hooked to one Deco unit to the FIOS Router of Verizon  in basement the house. This is a Verizon       1 GB sm( net speed ). Detached the existing 3 pack Google Mesh wifi( old models).

Deco M9 plus  was configured within minutes and prompted me to download latest FW version 1.5.1. Reluctantly, I proceeded, downloaded and installed th FW. 

Immediately,  I checked for speed which showed a Download speed of 670 mbps and Upload speed of 710 mbps. I went up to the farther end of Sunroom in the next floor and checked the speed, which is 650 mbps for DL  and 690 for UL. The speed given by Google Mesh wifi (1200) is just 230mbps DL only.

I hooked up the other 2 units and installed the FW.

In my house, 2 persons are Software Engineers , working from home. Besides, two TVs are using the internet service.

Till now I have not faced any issues.