I’m almost finished with my Invisalign process. First set of 24 aligners made great progress, but some stubborn canines refused to move. I’ve since had two sets of “refinements” (15 trays, then another 10), which have helped, but my teeth still aren’t exactly straight. So about 50 trays in total, for about £3.5k (central London).
It’s taken over 2 years and, while the difference is great, I kind of wish I had just got metal braces and done it properly. The issue I have with Invisalign is that, if any teeth refuse to move as projected, any subsequent trays no longer fit properly and therefore stop working. The answer would be to rescan at that point, but my dentist insists of just finishing the set of trays - which is a massive waste of time.
Check the price of subsequent sets of refinement trays (expect to need at least one refinement, as your first set won’t work exactly as projected), and be realistic about what can be achieved.
Oh, and they are very much visible, especially if you have “attachments” (lumps of composite stuck on your teeth, to help the trays grip on your teeth). They’re just subtle enough for people to ignore rather than comment on.