I used one with my daughter, but when she got a bit older I started microwaving them for 30 seconds and found that the handiest way, so I think I'll probably just go straight to that this time, using cooled, boiled water from a jug in the fridge. As someone else said, it's not the recommended way, but it works for us and I'm happy with it. Still have the bottle warmer, so can always use it depending on how things go.
I have an Avent one, and one thing I'd say is that with me using it upstairs beside the bed, the odd time I would forget to switch it off out of pure exhaustion and that really worried me!