Garrett claim that both these models have a form of discrimination,that is highly debatable infact i would say that is a slightly misleading claim but i wont dwell on that one.
If it was me i would look at either the Seahunter or even models made by Whites,if you are planning on doing beach work for most of your detecting then possibly a Minelab Excalibur could well be the better machine as not only is that waterproof to fantastic depths it also offers discrimination as well and was designed mainly for beach work/diving,but its also a machine that could/can be used inland as well.
But if you wanted to use a machine for beach work on just say the odd days holiday that type of beach detecting then the C-Scope 4pi model is about as good a deal as you can get,for the price i dont think that you can beat this machine for beach/surf detecting albeit its not a waterproof machine but as most folks dont tend to dive with them totally underwater then this C-Scope could be worth a look.
One of the best all time VLF beach detectors is the Minelab Sovereign range but just had production stopped in the last few years,still plenty of them around 2nd hand but the Minelab Excalibur range is still in production,if i was to go fo a beach machine that was within your main criteria of being waterproof then the Excal would be my choice but it falls down on your PI option.
What ever option you choose keep us updated,but if i am honest and also the amount of folks who do beach detecting the Infinium is not the preferred choice,that is upto you to decide and decipher what i am saying
Only this morning I went ahead and bought it.
I have the At pro and I love it but it is not much good on the wet sand, so I was looking at getting a PI and I love the idea of any detector that is waterproof.
During the summer when out with the Atp the weather was good and 3 fields away from the car the heavens opened, it wasn't just a light shower but torrential. I was wet right through but had piece of mind knowing my detector was OK.
So when looking at a PI " waterproof " was the first and most important thing on my mind after all I intend using it solely on wet sands and the dreaded Black sand.
I want my detector to be waterproof so I can on detecting without worrying about getting wet and killing it, to me the beach means one thing " WATER " and plenty it.
Anyway I got it cheap and its in perfect condition complete with waterproof headphones a little dearer than I could buy a new cscope for and it is most importantly 100% waterproof = peace of mind. I would have paid double the price if I had too.
I will have it in a couple of days and am going to try it out the day I get it and I will take the next day off depending on the tide times. I will let you know how I get on with my new toy :-)