I wouldn't expect to see any measurable MPG improvement over a well tuned carb for this application.
Maybe for a throttle body, but for MPFI it's a huge difference.
You can expect to see a difference over a well tuned carb. Maybe not right now. It will likely be when atmospheric conditions change and the carb needs to be retuned for perfection. It will certainly happen if you go through big elevation changes.
If you keep your car close to home you might not notice a big difference but the subtle stuff alone is worth it.
