When looking at the adaptors make sure you check the mA rating. There's 1,000 milliamps to an amp, so if you see the rating as 500mA that's 0.5 amps or half an amp.
The 12V USB adaptor I use has two ports one with 1A and the other with 2A and it works great.
The problem isn't that the good ones aren't inexpensive, the problem is often you're not aware of what is important so the companies sell you equipment which really isn't suitable to your needs.
If only Aldi provided a clear picture showing the rating it would be much easier to make a decision. At $4.99 if the rating is 1A I'd be very happy to buy one, or perhaps two of the units. I'm using 12V power now for more of my energy needs so these adaptors can come in handy.
With the 12V sockets, do be careful not to try to use too much power. I'm often reluctant to use some 12V devices in the car because one device (a scrolling LED sign) ended up damaging the electronics in the car and to get that fixed, wasn't a bill I was looking forward to. Luckily or unluckily, the car was in an accident and didn't need to be repaired. Make sure you understand the power limitations of your devices and your car's wiring.
UPDATE: 1 July 2015
The USB ports on this device are 1A and 2.1A. This is the power level of another adaptor I have which works well, so I was happy to purchase two of these from Aldi.