I had one, it lasted for 4 weeks then died. It did a great job of "sweeping" the DSB, but is a very clumsy swimmer. If you have a lot of LR, it could get stuck and/or tip them over onto other fish.
Hope this helps...
My opinion is that a single Horseshoe Crab can kill a perfectly good sand bed in less than a month.
Another opinion is that they need a lot of food once the sandbed is depleted of worms and they get up to 2' long in kless than 2 years. These are not small critters.
Very cool looking though
I have had one for a couple of months now and I just thought it was cool. I have liked seeing it swimming around and have had no problems with it. I don't know about the killing of a sand bed but it does add an interresting thing to the tank.
Koranman
I had one. Didn't last long and was a pain in the butt. It was constantly swimming and died being sucked up into a powerhead.
Waste of time and money.
Adam
Well, gee... if you'd like a five foot long crab in your aquarium, go ahead! Horseshoe crabs are one of the few organisms that will NOT stop growing when its habitat gets too small. Probably because they stopped evolving several million years ago.
(Although they do grow rather slowly)
I had one about 3" long for about a year did not seem to grow much but every time he went for a swim i had to turn him over will not get another one pain in the butt