Internal gearing has its own issues. While it's generally reliable, there are small parts inside them, and things will break occasionally. If an internal system breaks, your ride is over. No bike shop is going to have a replacement unit in stock, and they certainly won't have parts in stock, or expertise, to repair it. That might be a pain if you're 5 miles from home, but it's a vacation-ender if it breaks on a tour.
As an aside to the "small parts" issue - I've heard stories of some e-assists putting too much power to the chain during shifts, and breaking either the chain or the internals. It's probably a good idea to not shift under power, even when the mfg says it's OK.