I've been trying to diversify and be very regular about my feedings. since it's not a daily thing, maybe set a reminder on your phone for every two-three weeks or however frequent you'd like to feed.
if you're worried about feeding a whole non reef safe star fish, put your shrimp AND the star in the sump while he eats, then throw your shrimp back up top when he's done with his meal. I originally started doing this because they leave the starfish "skeleton" behind and I have black sand- it made a mess.
I know a person who bought 20 CCs to keep in his sump and just rotate through legs. they just DONT regenerate fast enough for how much your shrimp needs to eat. he'd make them tripods and then just feed the whole thing.
the first one I ever had I trained on frozen. he ate legs no problem, but he did die prematurely. I can't 100% for sure say it was the food source though. just an experience.
although I usually buy whatever is cheapest, I do make a point to change it up. my local LFS sells astrinas 12/$5. obviously CCs are usually cheap, and I've found linkias for $10 at swaps.
always check your local groups and forums. a TON of people buy non reef safe starfish unknowingly and just want to get rid of them ASAP. perfect harley food. also, hit up your reefing friends! I have a few friends who have astrinas everywhere but do not have a shrimp. they happily give me handfuls every time i visit. I throw them into my sump so they can attempt to repopulate and I can keep track of how many I drop in and what the shrimp is actually consuming.
lastly, pay attention to him! most harlequins will hide while they are happy and full. if you see him out crawling around the front of the tank, he's begging for food! just because he's tiny, doesn't mean he has a voracious appetite! i remember the first time I fed my little guy an entire CC. the star was climbing up the wall, upside down, while the shrimp (no bigger than one of his legs) was riding on top of him eating him. lol.