Ebike: Bafang add-on behavior and user's manual?

I've got almost no experience with e-bikes, but a good (if somewhat
distant) friend had a Bafang mid-drive unit installed on her favorite
bike. She's an avid and experienced cyclist. In years past she's ridden
across the U.S. at least three times (and walked it twice!) and she's
toured in several other countries, but she's getting older and wants to
keep doing rides with friends.

I believe the model she had installed is a Bafang 215. After some trial
rides, she's afraid to use it, and asked me to test ride it and offer
advice.

Unfortunately, I had limited time to do this yesterday. But fussing with
it for perhaps 20 minutes I was pretty skeptical about the thing.
Obviously, it adds a lot of weight, and will probably make it impossible
for her to heft it into the bed of her pickup for transport. But there
seemed to be rideability problems.

Most disconcerting was a tendency to suddenly surge. When coasting, if I
twitched the cranks forward a bit (applying no torque) the motor would
suddenly drive the bike forward. IIRC this was worst in a high assist
setting, but present even at low assist. This occurred at times when I
was trying to maneuver slowly, such as at low speed, snaking my way
between obstacles, and was pretty disconcerting. It also seemed to delay
disengaging at times, driving forward for half a second or so while I
hit the brakes.

Perhaps there's a setting to minimize that? The handlebar-mounted
display screen has at least 20 different setting categories. But she
didn't get a user's manual, and I don't find one for that model at
Bafang USA or at bafang-e.com Bafang USA's chat was no help (maybe
since I'm not the owner?) and bafang-e has not yet replied to an email.
(BTW, she says her computer is down, and she's not the type to rush to
get it fixed.)

Another somewhat scary Bafang feature is a manual throttle lever.
Pushing this turns it into a motorcycle - or legally, I suppose, a Type
II ebike. But the acceleration is pretty startling, and could be a
problem if it's done accidentally. (I bumped the lever while straddling
the bike and it did a wheelstand while ramming my back with the saddle
nose.)

She really loves the custom touring bike on which this unit is now
installed. Any experience or good advice from those here?

--
- Frank Krygowski