It is that it is one potential place for things to go horribly wrong. Sure, checking the chamber first renders the act to be rather less problem, but it is still a potential problem area. If you get distracted, forget to check, or anything like that, people can be injured or killed. Even the most responsible person can have a bad moment.
I have one gun with that kind of design... I am always EXTREMELY careful when taking it down for cleaning. But the fact remains that it is a trigger pull that is NOT intended to fire a round. That by itself dangerous for the reasons mentioned. Not a danger that cannot be managed, but more dangerous than a design that does not require it.
I would not advise someone against such a design for that reason, but I would advise that the buyer be very aware of it.