@T-NT
While let's encrypt is great when compared to not having anything.
There are conveniences ~$150 per year buys you with an okay wildcard certificate. Certificates being valid for a span of years... Free revocation and reissue all day every day (versus a few times in a week). ...wild card subdomain support, you don't need a new cert if you roll out a new host on newhost.domain.com . Tech support tickets.
The conveniences and stability a paid SSL solution provides are likely more attractive to onion.io than saving $150. What is time worth? You have more of it if you are not dicking around with a certificate with more points of failure-- I know that. And I say that as a fan and supporter of Let's Encrypt. They are doing great things over there and have no reservations against someone using a Let's Encrypt cert-- when it makes sense to.