You might wish to review their Privacy policy, which inspires more confidence than Goodreads:

https://www.librarything.com/privacy

The site's also been around since 2005, so, that speaks well to both its longevity and its integrity. Of course, that's not to say they couldn't be acquired tomorrow and paywalled, but I think it unlikely.

I don't think I am particularly worried about a proprietary solution. If I am putting my preferences in the public, pretty sure I am giving up on some dimension of privacy. With books at least, it doesn't seem so concerning as long as the recommendations don't suck too much (I don't particularly rely on recommendations that much though). But of course, you never know!

I recently "kondoed" my books down to like ~2xx total volumes and once I had them all organized it only took me an hour or so to scan all of them into the LT iOS app. Very few wouldn't scan but those were mostly findable by manually searching. Having an up to date list of all my books is pretty satisfying and LT seems to have a decent reputation in the serious-about-books-online community. Even inspired me to schlep into the office to catalogue my work related collection.

Made me realize how many booksellers(especially used) put proprietary barcode stickers on top of the 'actual' barcode stickers.

LT is in the slow process of upgrading the interface to something newer/modern and especially with better mobile device support. The screenshots on their blog I've seen look like it is coming along nicely, and as a long time LT user I appreciate that they take their time on big changes like that.