The problem with MG soil is the time release ferts.I used to use it myself and have had success using it.but iv also had problems in late flower due to salt build ups.its unpredictable and therefore undesirable.stick to a soil you can work with is mho.The person asking the question is obviously new to growing so why tell him to use a soil that gives even experienced growers fits?
The time released ferts are of trace amounts .020 or around there. It is simply a microbially enhanced soil the amount of N-P-K in the soil that is time released is negligable .020 as compared to the 20.-20.-20. used for vegging.
Once again the problem with the soil is lack of oxygen flow due to compaction and staying wet all the time that causes root rot. This is easily fixable by adding more perlite. Problems solved.
Your friends buiild up was most likely caused by not having enough perlite mixed in there the roots stop getting oxygen and stay wet all the time. If you dont add gross amounts of perlite 50/50 you WILL have problems, If you add enough perlite you will NOT. Simplee end of story. Nutes are nutes, if you add 20.020-20.040-20.018 your plant will not suffer for it unless it can not get enough oxygen to the root then it WILL burn.
i am an experienced grower never had a single problem with MG or its nutes, Must be something they are doing if they are having fits.