All of the windows on my NL are Heki and we open and close them every trip, but very carefully. The skylight has been opened for ventilation in hot weather a number of times over the eight years that I've owned the camper. Nothing has broken yet, but I've read many tales of woe with Heki and they make me nervous.
I called Dometic to see about ordering some spare latches and parts. The automated phone system referred me to Camping World. Called Camping World to find that they are unfamiliar with Heki (or the person who answered the phone was). I've got Leisureshopdirect in the UK bookmarked and will see about ordering from them.
Meanwhile, tying it down gives me some peace of mind. ;)