I get my stuff from Grin Tech (ebikes.ca) in Vancouver, BC. It helps that I am up there some as I have a son that lives there and am able to go by their facility. They are really all about kit bikes and have taken the time to document tons of info about e systems in general. Justin Lemire-Elmore is a nice guy and this, caution long, interview highlights his knowledge:
Since this interview they have moved to a larger facility which they seem to do every few years as they are expanding at a consistent rate.
Their All Axle motor is what I have on the silver bike and it is about 4 lbs. lighter than the 9c on the black bike. I like the built in torque arm on the AA but haven't been able to take advantage of the thru axle compatibility yet due to lack of fork selection in my price range, as in cheapish. Many are put off by front hub motors because they think they will tear apart the fork and this if they are setup up properly with a torque arm is not at all true. The black bike has about 2k on it and has a BD CF fork with CF dropouts and there is no discernible wear on them at all. It is kind of a pain to have a nutted hub and bolt on torque arm though and the way I have the AA setup it is tool less in and out. Just have to let the QR go, give it a few spins to get past the lawyer lips and undo a few wire connections.
I use their 35A controller set at 25A as that is all the power I need (52V x 25A = 1300w) but truth be told I torched a 25A controller doing some serious hill climbing in hot weather last summer and this one has never even gotten warm.
I have one of their 11Ah (10.5 actual) HL shark batteries that I can get 18 miles full gas or in the 30's mostly. Really dependent on my mood, time and terrain. I like the looks of their 16.5Ah battery of the same design which would extend my range by 60% but I am waiting for a 21700 cell battery to show up here hopefully early next year. Most rides and time to ride the battery I have does the job. Rarely do I get done with a ride on one bike and then come home and head out on the other. Much like the way the manufacturers are specing two battery systems for shorter tripping it doesn't make sense to carry the extra weight of too much battery. But I can think of some rides that it would be nice.
Their Cycle Analyst III is a must have tool IMNSHO. It is kind of clunky looking but the control it allows you over the bikes controller and the super accurate readout in watts and Ah's while on the go makes it head and shoulders over most displays simple Voltage readouts which it also has but I don't use as it fluctuates too much.
As I liken riding my e bikes to riding a tandem with a really fit stoker I would imagine that on a true tandem with a front hub motor it would be more like a really fit captain with two stokers

. I wouldn't mount anything heavy in that trunk bag though, i'd go with your lowest bottle bosses for good handlings sake. Tandems can be whippy enough without having that amount of weight up there.