I've switched to Amber a couple of weeks ago and so far it's EARNED me a little over $50, plus they've given me another $19 credit for a slight issue they had one night (cost me about a dollar in earnings and I didn't even ask for a credit, just woke up to find a sorry email for something I didn't even notice) plus another $30 referral credit. So in all I'm in profit almost $100 already, not even considering what I would be paying another supplier.
I'm VERY happy with them. Note I have a Tesla Powerwall though, so I'm able to shift my usage to take full advantage of arbitrage opportunities etc.
Also most days have significant periods of 0c/kw or even -1, -2c/kw where I'll be able to take full advantage and charge my car once it arrives.