The only really I said they are aggressive is that they can voracious eaters. They not only eat detritus but they are definitely carnivors too. I've had fish die or food drop to the bottom and they all over them in a couple minutes.
Don't get me wrong they are beneficial, but I think it's prudent to put in a smaller quantity. I've never really observed it, but I'm sure they're similar to sand stars where they can devastate your population of beneficial animals in the sand bed.
I've had some in my tank for around 2 yrs now and they do a good job keeping the sand clean, but I only have 5 to 7 of them in my 135. I think if you get that many, there won't be enough food to go around and they will start dying off. Anyways, it couldn't hurt to start off on a smaller quanitity and then increase them later. good luck.