Ah, the infamous Bulgarian Method developed by "Uncle" Abadjiev.
First, I agree with
@Kettlebelephant that Pat Mendes is not the best example of success using this method because he did use PEDs and the Broz method is the Broz method, as
@Geoff Chafe mentioned.
Second, the "true" Bulgarian Method is somewhat of a mystery. It's not just training every day but doing multiple sessions a day. And by multiple I mean not just two but up to four training sessions per day. There is a rumor/anecdote that Abadjiev developed this method not for its training effect but to control his lifters. Unlike other athletes, weightlifters can be a little "looser" with their non-training time and still be successful. They can eat crap, especially the super heavies. They can smoke. In fact, there were stories that during the Olympics in the '80s and '90s the Turkish, Greek, and several East Bloc lifters would hang together outside between the snatch and the C&J to smoke. They literally smoked at the event! Don't see too many marathon runners stop to take a smoke. I'm sure these guys also liked to have a drink now and then. Of course, eating crap, drinking, and smoking will eventually affect the performance of a weightlifter, so it is understandable why a coach from a country where eating crap, drinking, and smoking are cultural norms would want to control his lifters' entire day.
Third, there was another rumor that Abadjiev was told to either produce champions or lose his job as national coach. The method thus became "natural selection." Training multiple times each day will take its toll even on a steroid user. Only the strong, but physically and mentally, could survive. Those that did were the best of the best, and the rest had to find a day job while dealing with injuries. Abadjiev kept his job in a communist system off the backs (and knees and shoulders) of his lifters, just like a true robber baron capitalist. Oh the irony.
Fourth, the method was applied to the Olympic lifts. Olympic lifts can be dropped so they have no eccentric component. It's the eccentric that causes the most muscle damage. The only lifts with an eccentric that the Bulgarians did were back squats and front squats. The Bulgarians did the classic lifts, the power versions, and front and back squats. That's it. While still tough, this is not nearly as bad as trying to do all three powerlifts multiple times each day.
Having said that, I agree with
@Steve Freides that frequency is good. I also believe that "experimenting" with different training systems is good provided it is done intelligently. You also seem very curious about the Bulgarian method. This curiosity will not be satisfied until you try it. So here are my thoughts:
The book by Matt Perryman is good.
Frequent lifting does, in a way, actually prevent injuries. How can this be given all of the injured Bulgarians? Because you will not be able to train multiple sessions per day if you have a regular job. There is a dose limit here. Even Broz limited sessions to no more than 3/day (I think). Glenn Pendlay, who also had his own variation of the Bulgarian method, used no more than 2/day and gave his lifters the weekends off.
Everyone makes a big deal that the Bulgarian method has you max out each day. But this is a very mellow max. Even Abadjiev didn't require his lifters to work up to an all out max during the sessions (again, rumor has it). If you're popping caffeine pills, sniffing ammonia, and having your buddy slap you in the face before your daily max, you're doing it wrong. You'll go days where you'll hit the same weight for your daily max. This is going to take discipline on two almost contradictory levels. You'll need discipline to push yourself to go lift every day, especially after five straight days of the same daily max. While you'll need to push yourself, you'll also need the discipline to back off. So what if you've hit the same max for the past week?
When I was Olympic lifting and in desperate need to improve my snatch, I went two weeks where I did nothing but snatches and front squats each day with weekends off. After a few days warm ups were quick since it seemed as if my muscles were in a constant state of being "prepared" to train. By contrast, if I train squat once a week my legs seem really stiff and warm ups take some time. This is probably the reason behind the injury prevention thing.
I was tired and hungry during this experiment, but nothing bad happened. My snatch and front squat both improved nicely.
So, I encourage you to try this method. Just don't be a moron.