Fisker is still vaporware and speak about Solid State Batteries that currently only exist in lab environment. Fisker does not have any other business area where they deliver and this is their shot at it.

Tesla roadster however, as shown in movies, does actually exist even though there still are things not yet ready with the car. And they also proven that they can manufacture and deliver Model S/X in modest volumes close to 100k/year. This Roadster is hardly a volume car so they won't run into the same ramp up problems like with Model 3.