Pillpusher
Contributor
Their model is subscription/no advertising. (And of course the $19 is for a subscription, not to read one review...)
Not being advertising based has it's advantages, but also limits the number of people contributing. The liveaboards have a relatively small number of customers, and even fewer that are coming from the US and contributing to US oriented publications or sites. And only a small percentage of people ever leave reviews on anything. So yeah, statistically it's tough and it's hard to find reviews on a lot of stuff. For my part, I prefer to post reviews anonymously. And unless something has changed, Undercurrent won't let you do that, even as a subscriber. So I choose not to leave reviews there.
Honestly, I don't see a single advantage to it... At least nothing worth $19 considering how, as you mentioned, it lessens the number of reviews. Good point about the % of guests not being from English speaking countries. Though, take a place like KBR in Lembeh. Roughly the same demographics of visitors. Similar countries of origin. Around the same number of guests per week, or at least close. Yet, on TripAdvisor, KBR has 241 reviews, 208 of which are in English. Yet, you're lucky to find even one review on a dive boat. I have to think that the main difference is that one is a free site and the other wants it's reviewers to pay $19.