I don't find this convincing. It seems to me that updating that one line on your website should not take longer than e.g. writing this comment. Why would you think it has a significant tradeoff?

I think we should celebrate doing things which are better than not doing that thing, even if we don't know what the counterfactual would have been. For example:

• When a friend donates to charity, I show appreciation, not ask him how sure he is that it was the best possible use of his money
• When my relative gets a good grade, I congratulate her - I don't start questioning if she really prioritised studying for the right subject
• When a server is nice to me, I thank them - I don't ask them why they're talking to me instead of serving someone else

I appreciate that transparency might never be on the top of your to do list, and that might be the correct decision. But when an organisation is transparent, that's a public good - it helps me and the community make better decisions about how I want to do good, and I want them to know it helped me. 

Public goods have this slightly annoying feature of being disincentivised, because they helps everyone, often at the cost of those providing the good. In an ideal world EAs would all do it anyway because we're perfect altruists, but we still respond to incentives like everyone else. This is why I don't think we need to go around asking eg. who has sent the best funding applications, even though that can often be more important than being transparent. 

I'd love to talk about other important public goods that we should celebrate!