1) You don't need this if you have solar. Most states and utilities have pretty favorable subsidies for "selling back" energy to the grid. The utility is credit the feeding back to the grid at 100%. This device will introduce efficiency losses and it is expensive.

Unless you have extreme peak v. non-peak fees, I doubt this will save you money. Even at 20 cent difference, 7kW hours is a 1.40 a day. But that assumes that you could use all 7kW hours at peak times (you probably aren't). Also, you'll lose 10% going form AC-DC, you'll lose 8% on the battery, and you lose 10% going from DC-AC. That is about 25% loss.

2) If lots of people get them, the peak v. non-peak difference will collapse.