I would say safety comes first so good comments and feedbacks from other customers matter.In addition to that it is important to simplify instructions and make tools easy to locate and navigate through them. Newbies will also like 24/7 support to ask questions if any arise.
Luckily most of lead exchanges have all those benefits

feedbacks/reviews can be easily fake because they can be bought from different kinds of people in any parts of the world , so if i were you i wont start looking on them just to tell if the website or exchange is good or no good .
it is important to simplify instructions and make tools easy to locate and navigate through them.
user friendly sites are indeed more attractive especially if a newbie is accesing it but even if veteran and pro users like me will always prefer sites that is simple and easy to use when compared to fancy sites that may seem to be more confusing .
Newbies will also like 24/7 support to ask questions if any arise.
costumer support is another important factor to look on but a newbie friendly site do always come up with a q&a or faq section to answer some basic queries more faster .