I've got one for when I need internet access when away from the office or home. As expected, speeds are extremely variable even if you have a good signal. You're at the mercy of whatever is used as the backhaul from your nearest node to where the cell network bridges to the internet. Latency is varies between okay and high.

Despite the adverts, I wouldn't rely on one as your primary internet connection. If you're just using it when you're on holiday then it should be okay assuming you get a decent signal.