Key lock keeps the key the same no matter what you change the pitch by, as in avoiding the "chipmunk" effect but it dont work that well on vinyl turntables so ive read. Also if your tunes are both in compatible keys and are not too different in bpm then they should sound ok assuming you dont go past the +/-3% limit for both tunes, the problem is when bass doesnt blend, ive found some truly awesome mixes with one bassline turned off, i find it can sound much cleaner, but i much prefer (if it works) both basslines anyday.