Question about Lock Screen Replacements

[nwwolf1]

I was just wondering, when I use a Lock Screen replacement, say Holo Locker or Locker Pro I disable my stock lock screen and always see a noticeable lag in the lock screen appearing. What I mean is I'll press my power button to put my phone in sleep, then wait maybe two seconds and press it again and it'll just go back to my home screen and then two seconds letter the lock screen will show up. Is this just because it's not the stock lock screen on my phone and it can't run that fast? Or is it just a laggy app?