That's a challenging question
@Aunthugh. It would help to have a little more knowledge of the condition of the bike: dings, paint job condition, clean or grungy and how well the battery has been cared for. At 600 miles, that's still pretty low mileage; however, have you been able to confirm that by looking at the total miles on the display? Also, this bike & battery are now 2 to 2.5 years old depending upon whether the bike was manufactured in 2015 or 2016 - the bike's serial number often has that info contained within it. Look around the head tube and bottom bracket for a series of numbers & letters imprinted into the metal (with paint over it now) which may be a bit difficult to read.
What's the furthest you've been able to ride on this bike? I don't know where you're riding; however, on flat ground Magnum claims a 30+ mile range on a new 36V battery. If you have hills, figure less range and because the battery is at least 2 years old a little less range. Consider how far you generally ride now and that in another year or two you will probably want a replacement battery for this bike, a potential cost of $300 to $500 depending upon where you get a replacement or a rebuild. And even if the original owner says they've been good at keeping the battery maintained; I always take that statement with a fat grain of salt
, even with the nicest of people simply because their definition of proper care may not match what we would do at the shop.
Did you consider that the motor is 350 watts? That's considerably less power than your current Bafang mid drive, so will you be alright with that? Again the places you ride now will help you answer that question. In general, hub motors are more quiet than mid drives (even geared hub motors like this 8Fun motor) which I'm sure you like. As a reference, 8Fun motors are Bafang motors, so you know that you'll have good durability with the motor.
I checked Magnum's site for the
specs on the Ui5 to get a little of this information. Brand new, the Ui5 sells for $1599 (Amazon, some dealer still has some) to the original $1699 on Magnum's site. Magnum has moved on to the Ui6; however, parts are still available from the company and a shop that's used to servicing various brands of electric bikes should be able to help you maintain it.
If the bike was in immaculate physical condition and I knew the person wanting to sell it (a previous customer at our shop) and solid knowledge about the bike's care, then we might ask $900 - $1000 as a consignment item. However, since you're buying directly from the owner, I'dsuggest you offer a little less.