The Coonan has been around a long time. I have lusted after one for years and years but have never seen or held one. The grip would be a problem for me with my smallish hands so I have never pursued one. I do have a Colt Delta Elite in 10mm and that is enough magnum power for me. In fact, I rarely shoot reloads at the prescribed level because the gun twists in my hand when shot and is not all that much fun at those power levels. At 40&W (the 40 S&W is just a 10mm short) power levels it is a lot of fun to shoot. The 357 Coonan probably is not all that much fun to shoot with the sharp recoil of 357 mag that I feel in my 357 revolvers.
Rimmed cartridges are hard to feed from magazine as the rims can get all tangled up but the Coonan is not the only centerfire gun that shoots rimmed cartridges larger than 22 rimmed cartridges. S&W made a Bullseye gun from their Model 39 that shot hollow base wadcutter 38 specials. It was the Model 52. The bullets are seated almost all the way into the case with a light crimp to roll the case over the end of the bullet. They feed fine and the is uncannily accurate (it was for Bullseye competition). I love mine but they are very expensive on the used market, if you can even find one. I looked for years before I found mine and amazingly I found two to choose from at the same dealer!