I've shot a number of elk with slick tricks, and another 7-10 at least with Hellrazors (very similar to VPAs) and never had trouble with penetration, or blood trails. Most fell in sight so no real trailing needed. Slick tricks work well, but I prefer COC type heads over them as if I'm faced with a frontal shot, I have no worries with my slow setup. Slick tricks are not what I would call a good penetrating head unless you're talking the vipertrick but its a small head and I used my last one two years ago.
Exit this year, he didn't go 20yds after the shot, and arrow went though like butter. One thing nice about those types of heads is you can shoot them to see how each flys, and then simply touch them up.