PBO does work but makes the processor get considerably hotter and therefore requires better than stock cooling to get good performance results.
What is 'safe' is personal and depends on individual tolerance level but as far as I'm concerned PBO is perfectly safe since it doesn't involve fixed voltage and frequency overclocking. That means the boost algorithm is able to protect the processor by lowering voltage and frequency when it gets too hot--which explains why better-than-stock cooling is essential to reap the full benefit of it.
But whether it can be considered effective or not is also personal as it depends on expectations. In general, AMD boost algorithm manages to eek out almost all the performance the processor is able to deliver, whether in lightly loaded/cool operation or heavily loaded/hot. That means any form of "overclocking" only results in marginal performance improvement when properly bench marked.
In short: the era of 20-30% higher clocks, and performance, from an overclock is a thing of the past so adjust expectations.
This my reality check since I build new pc. It was long time so its much different now.
Ryzen master is the good but I not use it as much as I should. For now I am not the fan of PBO from what I read. Voltages discussed and the resulting heat is my reason for this. For others this completely acceptable. So I not use PBO or Automatic settings that why I guess I not a big Ryzen Master user. For me I like overclock and like tinker. Gains have been almost nonexistents. These cpu run amazing hot so I still trying to get used to that. For me advantage to OC is I turn voltage way down and heat drop along with it so fans not going crazy playing good game.