Oh come on Minn. By "common standards" most of what we do to live on a small boat is equally unusual. That's a silly criticism. The commercial composting heads function almost identical to every other toilet. Sit, open a trap door, let 'er rip. What's so different? What's gross?
You are absolutely right that living aboard has many unusual requirements compared to living ashore. Most of us would look at my master stateroom, with separate shower and head, a centerline queen-king bed and built in settees on each side and consider it a magnificent suite. Almost every non-boater that's aboard thinks it looks like a sardine can, with the aft cockpit above the mattress and only about 20 sq ft that one can actually fully stand upright.
I'm specifically referring to these non-boater's perspective, not sailors, which one may have as guests aboard. We have a ton of them every season. Knowing that a weeks worth of turds are just below that trap would clearly disturb some of the delicate landlubbing flowers we have visit. Then, what about the toilet paper? Do you require it be bagged or can it go in with the compost? Any skid marks before making it through that trap door that have to be cleaned? Any previous urine to gurgle in that bottle they have to aim for? Presumably, you want them to turn the compost when they're done, which will be a different experience from flushing. Unless both delicate and dumb (good entertainment if they are), they will realize they are just mixing it in. Any chance they just won't follow these rules and pee on your compost?
Better still, stick with your standard marine head. They work fine. I'm not saying everyone should switch to composters. There are significant benefits (for those who are not grossed out by it all), but it's not perfect, and there are some downsides. Just like with most things in our sailing/cruising world, there is no one right answer for everyone.
I agree and I'm not trying to talk anyone out of a composter. Just adding one of the issues to consider. Guests may be grossed out.