I accidentally did something along the lines of the Bulgarian method for a few months - I say accidentally, because I came from doing generic bb'ing stuff and had no concept of programming for strength and just kinda made it up.
For me in that situation, it worked fucking well - healthy gains in strength, despite the fact I was dieting down at the time and dropped ~6kg. But I should add I also do intermittent fasting.
Working up to handling maximal weights ~6 days a week did wonders for my confidence and technique. And once adapted honestly it felt less taxing than 531 is for me now, which has me often feeling a bit 'beat-up' and far less confident handling near-maximal weights.
After another few cycles of 531 (with a bit of modification), I intend on doing the Bulgarian method for a 6-week block, and then evaluate what to do after that.