I've had both...Performance is pretty similar. I'm not a fan of either. If push came to shove I'd get the 350 over the CMP for the simple reason of coil selection.
Both are really easy to learn, the 350 is more customizable with its settings than the CMP, I'd say the 350 is more stable and less prone to falsing, the CMP's tones sound a 100 times better!
When you say beaches...you mean salt beaches? Niether one will work well in that environment because neither have manual ground balance capabilities.
Fresh water beaches won't pose a problem.
For the price I wouldn't recommend either. I'd be looking at Tesoros Silver uMax or the Cibola. Keeping in mind neither of those have manual GB either.
If you need a detector that does it all and want to do salty beaches, you are going to have to pony up some more money for a machine with manual GB adjustment!