Until and unless they do make the technology work, they are selling fantasy.
I... I don't actually understand why this comment got so many downvotes—and I'm 100% for cryonics. In fact, I agree with the above comment.
Is this a toxic case of downvoting?
I wrote a blog post arguing that people sign up for cryo more for peace of mind than for immortality. This suggests that cryo organizations should market towards the former desire than the latter (you can think of it as marketing to near mode rather than far mode, in Hansonian terms).
http://specterdefied.blogspot.com/2015/06/a-cryo-membership-buys-peace-of-mind.html
For those signed up already, does peace-of-mind resonate as a benefit of your membership?
If you are not a cryonics member, what would make you decide that it is a good idea?