Here are my three. I like the 600 the most. A few thoughts on it:
If you get one, rule #1 applies. Get new springs! They are available from Wolff and they are cheap. This is ESPECIALLY critical with these pistols because of their rather violent blow back action. A pistol with weak springs in it will beat itself to death in short order.
The recoil on these guns is rather unpleasant compared to other 9mm pistols of similar weight. This is mainly because of the grip angle, not necessarily because of the blow back action. There is a lot of muzzle flip. They throw their empties a long way.
When you disassemble the gun, do it in a small enclosed room or space that does not have any glass in it. These guns have the largest and possibly the strongest recoil spring ever put on an automatic pistol. If it gets away from you it can fly into the nearest mirror, in my case, taking the retaining collar and bushing with it. Once you get the hang of it, its easy. Another good trick is to drape a bath towel over the gun during disassembly.
Do NOT dry fire these guns! The firing pin is a two piece affair and the front piece is probably the weakest link on the gun. A simple way to lower the hammer on an empty chamber is to take a pencil and insert in into the barrel, eraser end first, point the gun up and pull the trigger. This is a good substitute for a snap cap, without the hassle. NIGHTLORD'S solution is even easier!
Like NIGHTLORD40K has mentioned, these are very well made, robust guns that will give good service for many years, but they are primarily a recreational shooter in today's world. Not exactly an ideal carry gun.
Standard factory loads are fine, but I would stay away from +P loads. They are loaded to a higher pressure than a 38 Super. 36,500 CUP for the Super and 38,500 CUP for the 9+P. Standard 9X19 is 35,000 CUP.
These figures are from the SAAMI website. I have to respectfully disagree with NIGHTLORD40K on this point. For recreational shooting there is really no point to shooting +P ammo anyway.
My gun likes hardball and some hollowpoints, in curious contrast to my 400, which happily feeds anything up to and including empty cases!! My 300 refuses to feed anything but standard 71 gr hardball! Go figure!
Finally, I have never had a stoppage of any kind, if the correct ammo is used. These pistols are VERY reliable.
Go get one! And enjoy!