We had one and although we did use it, it was a bit of a hassle.
Firstly, it was big and bulky so needs somewhere you can store it.
Second, although it had a plug-in cable for the car, we couldn't use our model when we were actually travelling, which seemed stupid. I wasn't going to plug it in when the car was parked! (Newer models may allow this though - this was a long time, when they were first launched)
Third, when it was on, it was very, very noisy. That sounds a minor irritation, but actually it became increasingly so!
TBH I found it most useful when I was defrosting our freezer at home! I'd run down the food in the freezer so that it would (mostly) fit into the electric cool box, and keep it in there until the freezer had finished defrosting.
If we needed something again, I'd go with a much lighter, 'manual' one, and use the frozen plastic boxes/bottles trick, along with tea-towels for extra insulation.