I did three ebike conversions using our old Trek MTBs and a more recent Motobecane 29er for myself. I used BBS02 mid-drive motors, P850C Displays, and 52V 13A batteries. I am very happy with my conversions. Myself, my wife and sister-in-law all rode quite a bit this summer on both pavement and dirt/gravel trails (not MTB-type single track trails). We rode in all kinds of conditions all the way from flat paved trails in Idaho (Cour De Laine) to steep hills in Western Montana (Trail of the Hiawathas/NorPac, etc.). The bikes worked very well. I am an older rider (68+ yrs) and found our bikes more than adequate to handle those types of rides. On flat trails the 52V battery would take my wife about 50 mi with moderate assist levels (30%). I never ran out of juice on any of our rides. The rides with moderate to steep hills that we did were 25-30 miles. We pedaled on all of our rides and didn't use the throttle.
I am admittedly a DIYer and did tinker with my bike quite a bit to get it right. I even re-programmed the Flash for all of our bikes to get a good workable ride for all three of us.
It depends upon what you want and whether you buy or build. As another individual mentioned, there are some very good ebikes for reasonable prices if you just want to ride. And there are many fantastic MTBs and specialty bikes that you can purchase for a pretty penny. We are happy with our choices based on our riding style, budget and the fact I am a DIY guy.