Hi
coopec43, as others have noted, the vast majority of compost head users are very satisfied with them. Oddly, most of the negative comments (which will come, no doubt) are from people who've never owned or lived with one. For some reason, this topic seems to bring out a lot of uninformed, yet strongly held, opinions. So brace yourself.
I view our Nature's Head as one of the best upgrades I've made to my
boat. But I completely that you can make your own for a lot less than the main
commercial options. That said, the
commercial options aren't much more expensive than a quality standard head. And if you factor in all the associated necessities (tank,
plumbing, fittings, thru-hulls), it turns out a composer is a lot cheaper.
I chose the Nature's Head because it fit well in my existing space, and its holding
tanks were slightly larger than Air Head (the one you have pictured). But I'm sure I'd be happy with either. C-Head is the other major commercial option I'm aware of. They use a slightly different approach by going with non-proprietary bins (which I really like), but they are ~1/2 the volume of Air/Nature's. This means dumping frequency is also doubled, generally speaking.
Chotu's comments about the urine bucket mirror my use. The NH tank is 2.2 gallons (if memory serves me correctly). Two adults, full time. We generally empty every two to three days. And with NH, the tank is translucent and the top third of the tank is visible, so it's not hard to see when it's time to dump.