The T6 Pro is a builder's grade thermostat. Here are the reviews from the Resideo Honeywell Home web site. One of the reviewers stated you can't disable recovery mode. That would be a show stopper for me.

I am not sure what is required for the demand defrost feature. Perhaps one of the heat pump experts can comment.

Thanks. I expressed my reservations about the T6 pro being builder grade and when I got home, he had replaced it with the new google nest thermostat with rhe mirror finish (GA01334-US). Have we jumped from frying pan to fire?

It appears the GA01334-US is the low cost ($130) version of the Google Nest thermostat. It lacks some of the features of the generation 3 model. The reviews seem to be generally good. I would ask if a C wire has been connected. If not then it may not work reliably, or if it does, you may be replacing batteries often. It will be the installer's problem, but unnecessary aggravation for you.

Here is Google Nest's response on the C wire requirement posted on Home Depot's web site:

May 19, 2021

Typically, smart thermostats don’t require a common (C) wire, but every system is different. Without a common wire, your Nest thermostat will charge itself through power sharing using your existing heating and cooling wires.

When there’s a C wire, it becomes the thermostat’s go-to for power backup when power sharing doesn’t work. This can also conserve battery life since the batteries will likely only be in use when there’s a power loss to the thermostat.

Also, Nest Thermostat (2020) has a backup battery. For systems that are not using a C wire, the average battery life is three to six months. However, depending on the Wi-Fi activity on the thermostat, it may be possible to extend or reduce the battery life.

@ Mike_Home, Thanks. A c wire was connected. See attached photo. What features woukd I be losing with this thermostat?

Here is the Home Depot page which has the reviews and a comparison of this thermostat and the Nest Learning model. Scroll down to see it.

Here is a recent negative review:

Jun 12, 2021

Not Nearly as good as the other Nest Thermostats

This is not nearly as good as the other Nest thermostats in the lineup. Coming from a Nest Learning Thermostat I was expecting this one to be more limited in functionality but this is very basic. It's not much of an improvement over a basic thermostat. It has a lower resolution screen, limited menus. Inability to control using Nest app. And lacks ability whatsoever to lock the screen. Rather disappointed with this product. Bottom Line: Don't buy this. Get any of the other Nest Thermostats in the lineup.

In my opinion the learning functions are not necessary and probably don't work reliably. I don't think you need the high resolution. I am not sure what you lose if you can't use the Nest application. The screen lock is nice if you to prevent someone from changing the settings.

Based on what I have read, this Nest has more features than the Honeywell Home T6 and it has WiFi. If it has been installed properly with the C wire it should be fine.

Thanks. Does the VS air handler and thedemand defrost feature need any of the thermostat’s functionality to work properly?

The blower speed of the air handler is set during the installation. The thermostat has no ability to change it. The on demand defrost is controlled by the heat pump and does not require any functionality from the thermostat.

The thermostat should control the 10 KW heat strips. Looking at the wiring I don't see how the thermostat will do this if the heat pump is not able to provide enough heat when the outdoor temperature is low. Ask the installer to explain this to you.

Thanks. When I scroll through thermostat settings, I see the attached. Does this change your opinion as to its ability to control the heat strips?

I found this video which you may find interesting: New Nest Thermostat $129! Budget vs Premium. It is a nice looking thermostat. It looks like Google Nest is going after the low cost thermostat market. It is eliminating features which most users don't need to save costs.

I looked at your wiring photo again. You have a W connection. Normally that is the connection which turns on the heat for a furnace or boiler. But for your heat pump, it looks like the W is what will control the electric heat strips. Usually the thermostat will have an Aux or E connection for the heat strips, but it seems this version of the Next uses the W terminal to work differently if the thermostat is set up for a heat pump. I will usually search for the installation manual to figure this out. But apparently this Nest has no installation manual. You have to use a smart phone to guide you through the installation.

Keep us updated on how well your new heat pump performs.

Thank you mike_home for patiently answering all my questions. We’ll see how the thermostat performs as the days and seasons go by.

This was a good discussion for me also. I learned something about the new Google Nest thermostat.