If you found one used, which is tough to find, be aware Candoo Pro is driven off the licenses. So if you bought one for $250 and all 4 licenses were filled, you'd need to buy a couple licenses for $150, bringing the price to $400. You can purchase new one with 4 licenses open for use at $400.
Something to consider, anybody selling one will likely have at least 2 out of 4 licenses activated.
You won't be disappointed, I'd say it's a must if you own a RFI or DI. I just have a couple carb models, it makes for a higher overall ownership satisfaction. I can program keys, track/reset hours since rebuild, and set or adjust static timing. You'll definitely get more out of it owning a RFI ski.