It seems you've gotten your answer. No, there is no single site with lots of good reviews of all liveaboards around the world. Researching dive trips to some places can be challenging.
Yes, Undercurrent costs something, though less than in the past when some of their information was not easily found elsewhere. But it's still a publication, not simply a website with the only purpose of "amassing a review database", although that is certainly an important part of it. Some people find that a few reliable reviews from frequent divers and the other content is worth a few bucks to them, and the piles of free reviews that tend to be from from casual divers (maybe not fake, but often not useful) or people with agendas are worth what they paid for them. If you don't want to subscribe then don't, but there's no point in continuing to whine about it. It is what it is.
The reason you aren't finding reviews for the boats on TripAdvisor is because the people that take liveaboard trips like that are more serious divers and will rarely post a review of a trip like that on a general purpose travel site like TripAdvisor, or use it for research. It's not the right venue. If they post a review they will do it here, Undercurrent, other dive-specific boards, maybe even a personal blog. Some of the large dive travel agencies may have resources that are not necessarily biased (even the simple fact that they book a boat - or not - may in some cases tell you something.) If you haven't found the info in a google search and some digging from whatever bits you find, it's probably not sitting out there.
Yes, it's polite to do your homework and not ask the same old things about a common place that has been reviewed a zillion times. Or give a list of every boat in Indonesia and ask which you should take. It appears you've done your homework best you can and not found any info to narrow down your choices more, so just ask already about your shortlist of boats. It's helpful to tell what's important to you. Questions here about specific boats may catch the attention of someone who was on it or knows someone who was on it, and get you some answers. Some people don't bother writing reviews, or mean to but don't get around to it. But if they see a question they know something about they'll answer. You might also get a suggestion of a good dive travel agent that you can talk to and figure out which boat would work best for you. They will have been on some on fam trips, and heard back from customers they've booked, and all that info may exist only in their heads. I'm not inclined to use travel agents for say a Caribbean trip where information is usually easy to come by and booking is simple. But in some regions of the world, they can definitely add value.
