And what about this mining captcha - won't it stress CPU of users too much??
Hi! Just as two people have already stated here, the hardness of this captcha is adjustable. In any event, even if you have a small phone, waiting time should not exceed 30 seconds, with average time for our 512 captcha being 8 seconds.
During this 8 seconds you can type in your login credentials, or do things that human brains were supposed to do - and not solving captcha.