Most of the time.. beat counters are worth shit so don't focus on those! if you really want to master mixing you should learn to mix with your ears, its hard in the beginning but it will help you a lot
And th DJM-300 is a decent mixer.. at the moment I own a pair of CDJ's 100 and a JBSYSTEM classic 3 mixer, and it works very well.. I can't recommend any good mixers though, I don't know many