My brother-in-law had one a while back.
Rode real smooth.
Had good torque, just kept on a-chugging regardless of how big a load you put on it.
Was reliable - he put close to 10,000 miles on it, no problems I was aware of.
Started better than you think, all things considered. His had a 110 volt engine block heater, which did a lot of good.
Got amazing fuel mileage. He guesses double what his current Sportsman 500 (non-ho) gets, or maybe even more!
Plus, for farm or industrial use, you don't need 2 kinds of fuel, Diesel goes in your tractor, combine, ATV, backhoe, etc.

Now for the cons.

Noisy, yes, very much so. Makes the 2 cycle ring-ding sound of my Xplorer seem almost non-exsistant.

Heavy - noticeably heavier than a regular Sportsman (but I gotta admit it WAS heavy duty all around)

More than anything else, it was S-L-O-W. In a drag race with a 200 cc three wheeler with a weak engine, it was dead even up to about 35 MPH, top speed of the 3-wheeler, when the diesel, which had a top speed of maybe 36 or 38, crawled away from it at a snails pace. Before you make too much fun, the diesel had about the same performance loaded or empty, uphill or down. It just was the slowest revving thing I have ever seen this side of a 2-banger John Deere.