As i expected

even it looks good at first look and offer one button position marking which i guess can be useful for water hunting since in water is harder to find markers especially if u r not familiar with site that also became main disadvantage . Absence of screen make make it impossible to guide u to favorite spot without cell phone an if u need to bring cell phone in water why u need it on first place. Once i bring my so called waterproof Sony phone to lake wadding , when i finish it it was full of water even it was no more then 10cm submerged in water, i fix it at the end but this annulled value of gold i find . Since then i considered them just water resistant, maybe new cat s60 is game changer but it is little expensive to experiment with it.On land ur cell phone will suit u well.
There is already detector with this function but personally i never think this function can be useful until now so I guess next upgrade for CTX will be selfie camera so u can take pictures of ur finds on spot

However i don't think i will change my Excalibur just because of this
PS: I just realize that GPS probably will not work under water, and especially not salt water so practically u will get inaccurate readings if any.