The current Designer Help is less good than the old one (V8.5, NSF) . Only Bookmarks is a good feature . Searching is a real disimprovement; the results look sometimes as if the sort order was determined by someone rolling dices.
In the old help we could also insert our company specific developer helps (i.e. class description, server structur, ...) and in the Notes Client help our own specific help for our users . That's why we, the developers, currently use both, an old enhanced Lotus Domino Designer 8.5.1 Help and only if really needed, the new integrated one. If it would be possible in general to add your own help pages also inClient helps, Designer helps, etc., our users would have an easy to use and standardised Domino Help Center.