Like Kiwibird said, my guys would absolutely destroy their cuttlebones. For the longest time, I only had three budgies, which wasn't a problem. Then I adopt Ziggy and Alice, then the Montreal trio (Rumi, Lara, Pollo), and it became a problem. The girls would absolutely destroy all the veggies I put in the cage, and they'd turn a thing of cuttlebone into a pile of dust in a matter of days. The Manu mineral blocks seem to do the trick, as they only nibble on it when they want to supplement their diet, as opposed to destroying it for fun.
For sand perches, I have a plastic pedicure perch which I clean with bird-safe disinfectant or soap and water, and I scrub it with a toothbrush. With a Manu sand perch, I don't know what I'd do. Maybe put a bit of hot water with eucalyptus oil mixed in on it (like Spirit said), then once the top layer is somewhat saturated, use a toothbrush to scrub off the poop and food. Then I'd rinse it in some cool water, then gently pat it dry. I know with cholla perches, they're a pain to clean. I spend at least 8 minutes cleaning one of those puny things. You need to use hot water, toothpicks, and you need to bang it against the sink to get the garbage out of the holes. Hmm, maybe I could use my WaterPik (or whatever it's called) next time. Great idea! Everyone should use WaterPiks to clean cholla.
I don't think there's anything inherently unsafe about rough perches (assuming they're made from non-toxic materials). The problem is if your bird is obese, inactive, disabled, has some sort of pre-existing condition, etc. My boys don't have problems with rough perches, but Rumi was obese and she tends to stand on the same perches a lot, so her feet get sore. However, her feet even get sore on platform perches, grapevine, rope, etc. Lara can have issues with those perches because she's so fat. And Samantha's ancient, so her skins probably more sensitive. Also, I don't recommend having any toys near rough perches, since your bird can get carried away while playing and not notice their feet are being scraped up. While I had my Montreal trio in quarantine, the girls became so OCD while shredding their kabob that they cut their feet on the bark on the kabob. Their feet were all raw (not bleeding, but it wasn't good), so I had to remove the kabob before they hurt themselves any further (both girls were morbidly obese, so that just added to their problem).