My own experiences with the Tiger Shark at salt water beaches were very good. I have not owned one for some years now, but I found that using the 10" coil I got very good depth in the wet sand and in the surf. However ( and in my view there is always a "however" when talking about vlf machines and saltwater beaches), not all saltwater beaches are kind to vlf machines. Some people say that their machine works well in black sand: the problem with generalising in these types of assessments is that there are different types of black sand. If the beaches you are going to detect have magnetic black sand, then the sand, combined with the salt water will make things very difficult for you and your detector if it is a vlf. A PI machine may have to be adjusted very carefully to cope with the conditions of some salt water beaches if you want even reasonable depth, so a vlf machine has little or no hope of coping in these places.
I would suggest that as well as researching prospective detectors, you also research the beaches you are most likely to hunt, even if some of them are 100 or 200 miles away.
I have not owned or operated a Sand Shark. HH