There are two problems with them. Firstly, they don’t disclose the amount of caffeine (and caffeine-like) substances they contain.
Unless they have changed their labeling following several deaths, that is still the case.
Secondly, they have been linked to at least two deaths where the COD was listed as “caffeine toxicity”.
The problem in each case was a fatal heart arrythmia (due to a previously undisgnosed genetic condition) so it’s not like everyone who drinks it will drop dead.
There are lawsuits currently making their way through the courts as well as studies being done to see how widespread the problem can be.
So, proceed at your own risk. But without accurate disclosure of the contents, it makes it impossible for anyone to judge how much is too much.
Google Lanna Hamann and Alex Morris for more specifics on the two deaths I mentioned.