Back in the mid 80s FAX, the predecessor of US Check/Airnet flew a handful of brand new Diamond I's. They supposedly got a deal on them from Mitsubishi and they used them to be a fleet leader on the aircraft, getting more time and cycles than it would normally accumulate in corporate use. They only operated them for a few years then they got rid of them for Learjets, if that tells you anything on how they were working out as freighters.