I've got several, one of which is an AkkuTrak. In all honesty, they aren't really worth the money. Occasionally they will find a leak that you hadn't found and save you some time, so you do get the odd win out of them. So they are ok. But a good 90% of the time, they won't find what you couldn't have found with just your ears, and you'll end up wasting more time desperately hoping the leak detector will pay for a bit more of its own price tag. 

Leaks do correlate with experience. When I first started, I used to double bag everything and leave the pump running on the second bag after the infusion, because I just always had leaks and could never find them. I've now been doing this professionally for 6 or 7 years, and I only get a leak once in maybe 10 or 15 layups. If I can't find it within 10 minutes of really pressing on the sealant tape, or listening for a hole in the bag, then I just pull the bag off and start again. It's quicker and easier than messing around for hours, convincing yourself you've found the leak and infusing, before finding it still leaks and you've wasted materials.

I have been using the Accutrack  for a long time and they work well for me.
I suppose it depends on experience, how good you are at making bags, finding leaks with your ears and using the leak detectors too.