My sense is that the awareness and participation is so low that ESCOs don't really make a difference. There's essentially no competition of the kind you see in other countries.
In Norway (my native country), there's a wealth of national providers, lots of competition, and it's easy to find the rates, and also super easy to switch. Pretty much everyone paying utility bills is aware of the choice, and most people don't choose their default infrastructure provider because they're usually much more expensive.
When I rented in NYC, I had the option of using ConEd or an ESCO. ConEd was always cheaper, because they already negotiate the best rates on the open market. I could choose a "green" provider, but I'd be paying 20% more.