I would suggest MK-677 only to people over 40 yo.. or even older than that. For people who are starting to have problems with low bone mineral density etc.
If you are younger it can mess up your hormonal system (insulin and GHS receptors).
There is also a study which says that it does not promote growth in young mice due to somatostatin RNA overexpression:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6240568/
Which basically means that your body is trying to fight and normalize the HGH level (with MK-677 your HGH stays high in blood for too long which is not normal).
So if you are young and use MK-677 it can even limit your growth velocity. HGH injections will have greater effects in younger people