As with ANYTHING, buyer beware...
I've used the free level of Model Mayhem since 2011 as a model... it has served me well... the vast majority of people I've met and worked with through the site have been really cool people, just there for the business of art and modeling... sure, there are creeps... hello, a certain proportion of the entire human population are creeps... be honest and direct, set your boundaries and stick to them, say so when something bugs you, meet in person for coffee first before shooting, and if ANYTHING feels the least bit off, LEAVE... bring ID to prove your age, and if you're under 21, DO NOT GO ALONE! And, for f*cks sake, don't do anything to impair your ability to advocate for yourself! Myself, I choose not to drink during a shoot, and I choose not to engage in anything that restricts my physical movement, or my ability to speak, with anyone I haven't known for a really loooong time... exercise prudent caution!
Model Mayhem is not an agency, it is not a model management company, and they never claim to be... it is just a networking website... if someone presents themselves as representing Model Mayhem to book you for a gig, do not respond, they're a scam and spoofing them...
Used with candor and appropriate skepticism, this site is excellent!
I will update when I try out the paid levels...