RSSZ more or less covered what I was trying to convey. True retention positions must be practiced. I don't practice them as much as I should but I've done enough of it, as it is, to know it works and needs to be done sometimes. I would probably relegate one of these firearms to a target-shooting role and leave my H&K for taking out the trash.
Trust me - "cutting the pie" is an outstanding tactic that should be practiced and practiced to death. However, there are times when it is better to peek from a retention in your weak hand (or cutting just may not be possible). Those are the times when you'll want a normal handgun.