IIRC, that unit takes a 1.5X60 belt. I think it also comes in 2X60 model, but buying all three wheels and changing them would negate any savings on the deal.
A 1.5X60 will work just fine for knifemaking. If you ever outgrow it, it will likely become your handle grinder, so the money will be well spent. Belts will be readily available from all the major suppliers.
If it is a VS type, I would get it in a heartbeat. New, they run about $3000.Some are single speed three phase, and easily convertible by only adding a VFD. If it is a single phase unit you will have to change the motor and add a VFD.
The single speed units run crazy fast at 8000 SFPM. IIRC, they sell a slow down replacement wheel that drops it to around 5000SFPM.
Things to check out:
Voltage and phase requirements ( some are three phase, and most are 220VAC)
variable speed or single speed
condition of wheels and bearings
does it run fairly quite, or is there a squeal or other odd noise
vibration
accessories