You have lesser trained individuals using more interesting medical equipment.
What could possibly go wrong?
Usually the staff of ALS ambulances have more training than regular ambulances. Obviously, they have less than an emergency room physician. What needs to be studied is locality and transit time. Does an ALS make sense in rural areas, where the nearest hospital is 30 minutes away? Does it provide a better mortality rate than a helicopter (which costs significantly more)? Or maybe, it's just the opposite where ALS is more effective in metropolitan areas where heavy traffic congestion can make a relatively short trip take a long time.
Even the article itself stated that more research needs to be performed before determining that ALS is better or worse. Limited data often limits the validity of the results. The known facts are that only 10% of people who have a cardiac arrest outside the hospital survive it, regardless of how they were transported there. There appears to be a higher mortality rate associated with ALS than not. However, it is not clear whether that is a causation or a correlation. To understand that, there are many additional factors that need to be taken into account.
For instance mortality rates are higher on helicopter ambulances, too. Does that mean they shouldn't be used? No, of course not. They have higher mortality rates because they tend to be used for more severe injuries to start with. Until a proper study is conducted, anyone's guess is as good as anyone else's.