From only a personal view and what I have encountered. I still have some HO and N items with electronics, sound, smoke, etc. Have never had a failure, and they still run. On my "O" scale items, its a 50/50 thing with almost every engine having a problem, or need to replace something.
I enjoy my "O" items, but with boards being bigger, same for the smoke units, and now seeing many features of steam whistles and depleting coal in tenders in HO. You would think larger would also increase better and reliable running?? I bet the HO will have a better reliability factor then "O" scale items.
Its seriously were I will be looking at what I have and re-considering my path into possible going back to HO.