It is a great concept, hopefully the first of many SMT's to be developed on the STEEM blockchain. Actifit does have a lot of issues for now, but as you said it is only three weeks old and they are putting huge effort into developing it. If they can fix the issues and develop it into a fully functioning health tracker to rival fit-bits or Samsung health it would be amazing.
I can see it gaining a big following and look forward to seeing how far it can get in the next few months.