Power converter for europe?
Buy a flat iron that's voltage adjustable (110 and 220). Then you won't need a transformer just adapter prongs.
Better to buy a cheap flat iron and curling iron in Europe when you land there. Indeed plugging a 110 volt heated apparatus into 220/240 volts is a sure way to kill it, sometimes with a loud explosion.
In my experience, power converters don't work well. It's better to buy something that works on dual voltage. That way, all you need is a plug adaptor. All electronics, like laptops, phones, iPads, etc are dual voltage so you never need a converter. There are also dual voltage hair appliances. Or you can buy one once you're there. The converter is the same for all European countries- it's 240 voltage. The plug adaptors are different. You can google which adaptor you need.
Firstly of course you need a converter so you have something that will actually fit in the socket (and Spain doesn't use the same plugs and sockets as the UK). But secondly, remember that Europe uses double the voltage of North America. If your iron only takes 110-120 V, 220-240 V will come as rather a shock to it and that's what happened in London. Voltage is the electrical equivalent of pressure in a water pipe. Push water through a pipe at a higher pressure than the pipe is built for, and obviously the pipe bursts. Same with electricity in a wire - except the result is not a flood, it's a fire because the excess electrical pressure makes your gadget heat up. So that's your answer - if your new iron shows on the specifications panel that it can take 220V, you'll be fine. Many things are made these days to take both voltages. But if it doesn't, you'll have the same problem again and it won't work without a transformer to convert the voltage down.
You read the power label on it. If it says 220v, you are good. If not, forget it.
You can buy it in Spain or at the airport.