I mean, there are some problems with NEST. However, I don’t know more details because I don’t use NEST devices.
Look here: NEST API support via Unofficial Nest Learning Thermostat API
Regarding Tado: You need the Tado Bridge for Homey to operate the thermostats. Central heating is not necessary if you only want to control the heating thermostats.
You can find out it here: Save Energy with Smart Radiator Thermostats | tado˚
However, Tado’s own comfort is already very good and you don’t necessarily need a homey for it. Some services are subject to a fee at Tado.
I used 2017/2018 Tado in combination with heating thermostats, as a stand-alone system. I can’t say which possibilities exist in combination with Homey. We moved in 2018 and now have floor heating, so I didn’t need Tado anymore.
I can’t help you with Netatmo.
Homey is Magic! 
If you want to make your house smarter in the future, I think Homey is a good choice. I have the Homey now about 6 weeks and am very satisfied. Before that I had another system for several years (Fibaro HC2) and haven’t regretted the change yet.
Because Homey supports different SmartHome standards, each one has its advantages and disadvantages, it would be useful to deal with the topic before. Some users were already disappointed after the first days, because allegedly nothing worked. The real problem, however, was that these users did not deal with the subject matter in advance.
