I have 3 chromis, also in my 90, and they are definite beggers. As soon as I stick my hand in the tank to feed the fish, they are right there picking at my hand. They also adopted my little percula clown into their school, so he thinks he's a chromis, too.
Some of them can be quite hardy too. about 3 months ago, one of the chromis got kicked out of the group and was beaten relentless until he was missing all of his right pectoral fin and he looked like he was filleted. I thought he was a goner, so I didn't bother trying to catch him out... needless to say, today, the only blemish he has is an itty bitty scar on his side, other than that, he looks great and is a trooper :-D
They are definitely worth the whole $3 I paid for them