There are basically three options:
1) The BAC-601 LCD Smart Display
2) A Cycle Analyst
3) A simple bike speedometer/computer
1) The
BAC-601 Smart Display comes with a mode button to allow the pedal assist level to be changed while riding but I have never been able to get all five levels to work as progressively as you would expect them to work. I found 2 levels were all I would use, but sometimes one level was not quite enough and the next level up would be too much. I must admit that I much prefer to use the throttle to control the level of motor assistance instead of the pedelec function.
The display is nice and clear and easy to see in in direct sunlight
(unlike my phone):
The battery gauge on mine is not very accurate, but it might be because I use homemade LiPo packs which are a different voltage to the more typical 24V, 36V or 48V batteries.
Also, you cannot use the Bluetooth dongle and the BAC-601 display at the same time, which is frustrating when the BAC-601 does not save your trip data when the battery is turned off, but your phone does.
2) The Cycle Analyst is probably the most popular display device used by the ebike community. It has an incredible amount of functions that is can be configured to suit the requirements of most riders.
This will give you an accurate figure of how much battery capacity has been used etc.
Further information and price etc. can be found
here.
As I have never used one of these, I don't know how clear the display is in direct sunlight.
3) There are too many basic cycle speedometers/computers to choose from so I won't go into detail on those.
But if your eyesight is anything like mine, go for a large and clear display unless you wear reading glasses while riding.
Alan