I JonathanK and welcome here.
Hard to tell how reliable it as, there is not much bike in circulation and few have a lot of kilometers. Mine has ~18000 km and I had to change the battery bus bars that where oxidized (now stainless steal), the rear wheel bearing, the front suspensions o-ring, the chain and normal maintenance.
I would say that my battery suffered from the problem I had with the bus bar because it was deeply discharge for several months
. When I am at around 60% of battery, if I accelerate fully for several seconds in sport mode, I get a battery low warning (voltage drop). Beside that the range is still the same, around 100km of cool driving, 75km when driving hard but no more than 110km (I am 1m79 for 95kg, I think it matters).
Also I have a oil/coolant leak at the motor, it's not a big deal, but not convenient. If the one you are looking at do not have the leaking, its a good find
If I were you I would check for this leak and do an almost full discharge of the battery to check the range approximately and good acceleration around 50%, 60% to see if you still have all power from the batteries.
Everything else could be done by classic mechanic and should not worry you too much. The electronic would be the main failure point but except for error code on the dashboard you will never know if its going to fail.