We have two Surface 604 Shreds. 48V 20AH batteries. We can get 60 miles out of them. Our longest ride so far was 44 miles. Lots of ups and downs. We have torque sensors so power is regulated by pedal pressure. We usually ride in level 2 0f 5.
I can guarantee you that you will get a workout on a torque sensing vs cadence sensing bike. We've had other road and MTB's for years and use Polar heart/fitness monitors when we ride. We know how many cals we burn in 1-2-3 hrs on average. It takes a little longer to reach the same cal burn but it's not like we have to ride twice as far by any means. I would say maybe 20-25% longer to burn the same cals. We're both in our mid and late 60's and find ebikes to be a great addition to our collection. Hot days really drag on my wife so we can now extend our ride times since she doesn't have to work as hard.
We ride our ebikes in places we would've never rode our other bikes because just getting to those places was a workout in and of it's self.
IMO ebikes are what you make them out to be. Use all the power and it's an easy ride. Drop the power and you get a workout.