Well here is an update on the cs4pi for you all ( I posted under the name Iber before, lost login details, hence my new account name :-) ) . I was using the old coil so there may be differences.
Firstly it's main advantage over vlf will always be on salt wet sand or in the water. After a few years on the beach with it, and having bought a G2 for the dry/inland, I decided to mod the cs4pi. Up to that point I had found two or three gold rings, a lot of modern coins, and even more rubbish, and a one and half ounce gold bracelet in shallow water too. All gold around here is 18kt (southern Europe). It isn't a pro set up but it works well. I would put "success" at a smaller part the detector, perseverance and learning as more important - so with the cs4pi you have room to do well.
So the mod to submersible. I used the basic idea from a DIY camera housing, with heavy pvc pipe. Don't ask me for plans, I built this a couple years back, but if I come across the original plans again I will post the link here. The original plans were for diving ( like 100ft), I only used mine to maybe 10 ft... in the surf, snorkeling. The new weight means it is usable but heavy on land, it is just neutral in the water. The circuit board etc. is taken out of its case. I was planning on magnetic control of settings from outside, but not nescessary, it is preset right and switches on/off with introducing the original battery throught the top. Not showing is the strap added on the armrest, and the added softgrip that covers... the grip. Gripping. I have a choice of wireless tdk headphone unit for the beach in one lid, or waterproof wired headphones with a different lid. It works like on the beach, hasn't leaked. Took maybe fifty hours to make.
Results are that on one beach I detect I have found gold ( usually rings) on every two hour snorkel ( not say where) , every single time. So for the fifteen times I have used it I have as many gold rings, about an ounce of gold, and some diamonds. Also many coins, a lot of lead.
Easy? No. It is a lot of hassle kitting out for that, wetsuits, etc., so it is for those adventurous. What is more, I tried two other beaches and found near to nothing underwater. That is to say you won't likely just head out and find worthwhile...but for those who enjoy this sort of thing...
( Remember that you void the cs4pi warranty by doing this, and a flooded detector doesn't detect. Also if the owner of this site wants to guarantee having the photo of the mod, then he/she should host it somehow, as I don't know how long the link stays valid)