Back in the 70's I remember seeing one once while quail hunting with my Dad. I was new to hunting then & we were both new to hunting in the Arizona desert. After describing the critter to Dad - told him it looked like a racoon crossed with an otter - he accused me of carrying something other than water in my canteen. Took a trip to the school library (the internet wasn't even a bad thought back then) to show him confermation of what I saw.
From what I've gathered over the years, seeing one seems like seeing a bobcat - not too likely unless your specifically going after one. I remember talking to a Air Force Lt (I was an Air Force brat living on base) who did alot of varmint hunting & said that he'd called in a few of them. It would make an interesting mount if you got one though.
I have only ran into a couple in all the years that I have been hunting in the desert of Arizona. That time all I had to shoot it was a .44 magnum loaded with 240 gr hollow points. I really didn't want to blow in into pieces so I let them wander off never to see another one since.
When I first learned of them I thought there were a lot more than there is. I think they are more of a night animal like a racoon though so that could be some of the problem. A .44 would definately be overkill. I was thinking more like my .17hmr but doubt I will ever get the chance at one.