It's not so much a brand of inverter it's whether or not the inverter allows you to island yourself. That is not send power to the grid, now those in rural areas who are relying primarily on solar power to charge batteries (often not high tech ones like the Powerwall) this isn't a problem, however with the vast majority of solar being hooked directly to the grid for the safety of workers they need to have circuitry to stop outputting when it doesn't sense line current anymore as this I'm sure this was the cheapest option for solar inverter manufacturers than having an automatic transfer switch that disconnects from the grid but still makes power, although those can exist they just typically cost more. Now there are ways to trick the inverter into staying on which I won't go into for various reasons, but I think the Powerwall (and other newer battery creators) does something like that (although I'm not absolutely certain) but the battery basically is the transfer switch that shuts off the power from the grid, so it's all good, compared to someone who may do a DIY solution which could kill people.