I have a bachelor pen with currently about 20 roosters in it. In fact I added three squabbling juveniles (more like opened the door and hurled their nasty bums inside and slammed the door after them with orders to settle it or kill one another I was fine with either outcome)this evening.
My coop is an old shed that we have partitioned into two rooms. A screen door separates the rooms, the smaller room going to the bachelors and the larger is the main coop. The hens and breeding roosters are in full view of the bachelors in both the coop and the run. The breeding roosters do exchange attitudes with the bachelors through the wire but nothing extreme. The bachelors do squabble with one another until they get their pecking order worked out but all in all separating the bachelors has helped their attitudes a lot and the hens appreciate not having the horny juveniles pestering them constantly.
IMHO, keeping them 'out of sight' of one another is overstated and in my case almost impossible to achieve given my coop layout.