I am a Sunsynk (Deye) user. Unfortunately, I can’t add much.
The Sunsynk does have some features which look great on paper (proper generator support with auto start and gradual ramp up, smart load, etc). But I don’t use any of that, so can’t really comment.
I really just use basic inverter functionality (here the time of day based settings are probably the most useful feature). I also read the inverter parameters and use them to run a basic automation system for the geyser.
So far, the system has been 100% reliable. The entire house (including geyser) runs off the inverter. Peak daily loads are about 7kW.
Factory support has been excellent (aside from the language barrier). I requested firmware changes to drive Earth-Neutral bonding relay, and they were implemented within a week and remotely installed on my inverter. They also supplied all the interface protocol documentation on request.
I have not needed much other support, but I am on the factory support WhatsApp group, and have seen how the factory does not hesitate to instruct the local agent to swap out any faulty equipment (which is fairly infrequent).
Probably the only complaint I would have is that it is a transformerless system. Without the ‘inertia’ of a big transformer, this means that power ‘blinks’ when I turn on heavy equipment (like a 3kW cut-off saw). Not enough of a blink to affect any electronic equipment, but still noticeable.
The other thing that would be nice would be remote management of the inverter. The default end-user software only allows remote monitoring, and you need to sign up as an installer to get management capabilities.
In the end, it was the cheapest hardware that met my basic requirements, but still had a decent warranty and good manufacturer support.