Griped and moaned about this when it was just weekly rerolls, but charging me a reroll to get rid of "Complete 1 Trial" and then charging me gold (2500, I think) to get rid of it again is just a bit over-the-top. NO MEANS NO! You're welcome to say "this is intended behavior and it's working as it should," but there comes a point when "No!" has got to mean "No!" and it should probably not cost me gold to say it again (and I'm not spending 10K to get rid of the resulting unwanted challenge). That system is flat out busted. No matter how much lipstick you slather on it, it's still a pig.
I'm fresh out of outrage, but I could muster up some amused annoyance if required.