With only 2 eBike excursions under my belt, I am by no means an expert, but I can say that they make a HUGE difference when pedalling.
Both outings were with my wife (non-cyclist) and more about the scenery than the ride or workout.
First one was the Lake Dunstan Cycle Trail. A 55km trail conisting of moslty gravel path or decked bridges. Did it on cheapo rental eMTB's. Ambling along in eco mode for the flats and going into Boost mode on the climbs (some of which were pretty big) made the ride very enjoyable.
Second was the Rotorua Forest Loop. About 31km of easy-to-moderate forest trail, undulating, plenty of roots, tight switch-back climbs etc. This time we rented some Scott Genius eMTB's.
The bikes and trails were far more rider orientated than the previous experience. I mostly just ambled along with the group (non-cyclists), but did take the odd offshoot to have some fun and test the bike.
As others have said, the ease at which one can race out of corners is amazing. The extra weight at a lower centre-of-gravity adds a sort of stability of the rough-stuff (similar to how a dirt like feels riding over bumpy tech stuff, but to a lesser extent).
Where I did find it lacking was in the air. Granted this was my first time on a "fun" eBike, so I have much to learn in the way of the different technique, but it felt dead in the air and required a lot more effort to get it there. Although it is 9kg heavier than my Trek Remedy, it felt about 30kg heavier when trying to playfully hop around on the trail.
So would I buy one...
Yes!
They are pretty darn fun, and for someone like myself (who has become a lethargic rider in the last few years), it could be the difference between deciding to drive the 45min (each way) to the local trails and enjoy a good few hours out there, or dissuade myself that the lengthy drive is not worth the 1.5hrs of gruelling climbs for a few brief (but fun) descents.
After all, I ride for fun.
Would I have it as my only bike...
No.
With fun being the main reason I ride, the dead-weight dynamics of the eBike when trying to be playful on the trail, or get some air, are a bit frustrating. As mentioned, I'm sure this would get better with time and practice, but on descents, I still prefer my Remedy.
So in an ideal world, I'd have R140k of fun money just waiting to be spent, and I'd get a Trek Fuel EXE (the "in-between eBike" and only about 4kg heavier than my Remedy). But as such amounts of fun money seem to evade me, and I cannot deny that I have considered selling my Husky dirt bike to fund such a toy, as realistically I'd probably get more use out of it than the dinosaur-juice burner.