If you go the Sand Shark / Tiger Shark route, you will likely use the Tiger on the dry sand of the salt beach (due to the typical junk content) and then switch to the Sand Shark when you go into the wet sand/surf.
On the CZ-21, you can use the same machine on both and simply re-ground balance when you go from wet to dry and dry to wet. That is a benefit.
I own the Sand Shark, which requires no ground balancing, and I use it on both dry and wet sand, going deeper than the CZ-21 can go. However, the Sand Shark has no discrimination, so you will dig everything. But heck, digging at the beach is no problem, except in the surf where it can become a bit of a chore.
If you want discrimination, I'd say buy the Fisher. If want to go deep and dig everything, just get the Sand Shark. The Tiger Shark is best for fresh water hunting.
Good luck!