As long as you give the piece a good shake every now & then to remove any accumulated detritus, I don't think it will cause any problems. It actually offers sort of a safe haven for a lot of the micro fauna within the tank IMO. Small ecosystems in each & every one of those shells.
It would also look awesome if it was covered with zoanthids or something like that.

 

Its a personal choice really. I never liked the look of those and went for all live rock, but if you like the look of them, it can be cool to see gobies and wrasses swim and rest inside of them. But like above, they can accumulate detritus so you will need to get a turkey baster or small siphon hose to get it all out.

The choice is yours!

 

personal preference. they do trap detritus, but if you have a blenny, blennies think that they are the greatest places ever.

G~

 

i decided to keep it. i will just try to blow all debri from each barnacle. I figure for a 10 gallon tank, there wouldnt be too many hiding spaces so this will supply that. My firefish found a spot at the bottom of it

 

One of my clowns sleeps inside his every night.
I do have to blow it out, either turkey baster into it, or pick it up and hold each hole in front of a powerhead. I read somewhere it's best to drill an exit hole in the back side of each hole.
My barnacle cluster is a lot smaller than yours.