1. Are expanders temporary until desired size achieved, then have to get custom gels to fill them once removed? Or are they as robust as gels?
There was a time when women would just get expanders and leave them in. And at that time, expanders got the same level of QA as regular implants.
That's when sales and marketing sat up and took notice. They wanted these women to spend the extra money for their 'final' regular implants. So they were able to get QA processes changed, such that expanders would only be warrantied for 6 months. A warranty period which isn't nearly as long for expanders as they are for regular implant would create FUD, which would help to create demand for regular implants.
So yeah, if you can get expanders to last 10 years, then that's great. There's no guarantee though. And regular implants have been known to fail sooner than their warranty period.
Source: a former BEA regular who used to be an implant engineer for a recognized breast implant manufacturer.