Since there are no actual data (2015-2016) in Russian except this question, I will write my opinion as the owner of that $ 99 subscription.
As far as I understand for myself, these certificates are only considered in very limited form as HR-gentlemen, since it is easy enough to take and solve specific typical tasks, thereby entering a certain top, while not having positively any real knowledge.
Quite another - when testing is carried out without prior notice directly at the interview. As far as I know, at least in one Russian company, this is the first stage of a technical interview.
For myself, I defined the use-case of this platform as follows:
If you are looking for a job, having <2 years of experience, then you quickly notice that each first organization (in an interesting professional area) requires an "excellent knowledge of C / C ++", and the metrics of this knowledge in the job description are usually not specified. Thus, you have 4-5 on a brainbench - you can say with some degree of confidence that the required degree of expertise is there and then to go for an interview with chances> 50% to get a job. Proof from LK.
PS With the right approach, the cost of an annual subscription can be miraculously reduced to $ 67 by promotional codes SUMMERSAVE
(applicable, it seems, since May 28) or SAVE70
(applicable, it seems, always). At least May 2016 was relevant.