The breakout adapter makes things simple - no need to worry about wiring things correctly or trying to locate the correct port / connector. You can use any RJ21 breakout cables / connectors - but then you have to ensure you connect your phone to the correct pair.
Many people here are seasoned veterans who installed many many telephone systems and can deal with things like amphenol cables, BIX blocks and patch panels with their eyes closed. Based on your questions, I suspect you don't belong to that category - so, getting the BCM50 breakout adapter would likely safe you some time.
And yes - the breakout adapter has RJ45 connectors, which are compatible with the RJ11 connectors on the phones cables - so you can just plug the RJ11 connector on the phone cable into the appropriate RH45 connector...