Right now I think derasa's are my favorite. My derasa has got to be 7-8" now and almost 5" across when it's open. Mine was bigger at 4 - 4 1/2" when I bought him.
I did see a 15" one for sale at the same time for 300 but that was out of my price range
29.99 isn't a bad price to add to an order -- maybe a little on the small side at 2" but my maxima was that size when I got it and it's maybe just a hair over 3 now and doing fine.
I personally think the derasa's have the best coloration and grow very fast compared to the others. I want some more clams too but I actually might have to take out live rock soon for my derasa.
If I were making an order yeah I'd get it. I'm done with online orders for hte year in North Dakota as I can't count on the weather lol... and I wish the LFS had something bigger than 2" clams for 60 bucks as well.