IIRC pre-covid when the program was quite new, customer could buy the batteries outright. Later on they added the lease option.

One of the issues with these is the limited storage capacity. While it is nice for short outages, there are sometimes multi-day events in the winter. I think the longest was in the late 90s from an ice storm and was over a week. If you have solar, less of an issue but not everyone does (though solar does have surprisingly good install base in Vermont).

I've not checked to see if GMP limits the install locations but do recall some states/munis trying to limit them to outside the home due to fire risk.