I found 6k "broken URLs" out of 20k, but scanning through them, I can often see why: the link is an obscure & obsolete page within a useful site, so I need to be able to open the link properties & edit (shorten) the target address, but there's no option to do this, and no indication of where (what folder or subfolder) the bookmark is, so if I want to edit the links I'm going to have weeks of work ahead of me - and I'll need to save the result!
Suggestion: If an address is "broken", search again minus the last folder/page & offer that as an alternative address if it is alive.
Otherwise it seems to work fine.