Well the chap that built the site is one. It looks like an excellent design to me, sturdy and well thought out. There is a lot of scope for the builder to adapt the design to their own requirements and building techniques. You don't have to use acrylic tubing for the hull, PVC would be tougher and cheaper (builders throw a lot of unused tubing out). You can scale the boat up or down to suit the tubing diameter and equipment you have to hand, for instance 11cm PVC waste pipe would result in a model 10% bigger, still a handy size, but a bit more space inside. The boat could be built as a dynamic or static diver, and for the latter you could use a water pump system if the converted syringe based piston tank looks too tricky, as you'd need a lathe really to build that bit.
Having the batteries release would pose a technical challenge. I haven't seen anyone do that to be honest, it would probably be easier to have a lead weight which could be dropped if you want some sort of emergency flotation, that's how the fullsize submersibles do it.