Don't make a decision on what I say, but I will put my 2cents down for the heck of it; Buddy of mine has avids on his trial bike and they lock up good! I would keep them on unless you notice the Shimanoes are significantly better but that's unlikely.
I'm an avid guy all the way. Run the new guides on my Enduro and elixir 9 on my dirt jumper. But I'm just getting into trials my self and the zoo Python I just got came with a cable disc brake and I'm swapping it for an slx. As a mechanic in a bike shop I know elixir ones are pretty poo. Cheaper shimano brakes are pretty good value for money and plenty of power.
I agree with all these guys, their brakes can work well sometimes. Im a mechanic at a Specialized dealer and they specd a lot of their bikes with those. Ive never had to bleed so many brake sets ever !! If they stop well and arent super noisey like every other Elixer, run em