I'm not in Peggy's realm of knowledge
but I'll help explain the components that make up the two different systems.
The electroscan consists of two or three pieces, depending on your installation
1. The treatment unit itself, which is approx 18" X 12" X 18"
2. The controller unit which is approx 6X6X3" and should bolt to a bulkhead.
3. A salt feed unit which in my case is approx 10" in diameter and 18" tall
It works by running a electrical current through saltwater to create a disinfectant chemical. The salt feed unit pumps a salt water mixture into the treatment unit as needed to produce the proper current flow.
The salt feed unit is a known problem area to Raritan. Hopefully they re-designed it, but as shipped from the factory (as of 1 year ago) it does not work reliably. I re-designed the unit and have been thrilled with the results after the factory could not make mine work properly.
The purasan EX unit consists of the following:
1. The treatment unit it itself, same exact size as the electroscan above
2. A controller unit, same approx size as the electroscan
3. A disenfectant holder (don't remember the exact size but small something like 6X6X6" bolts to a bulkhead
4. A air pump for the disenfectant unit
The purasan works just like the electroscan except that it injects a disenfectant solution into the treatment tank (instead of creating disenfectant from salt water) The way this injection process works is that it uses potable water to wet the disenfectant into a solution which is forced into the treatment tank under pressure. The pressure comes from a air pump that pressurizes the disenfectant holding vessel, forcing the disenfectant solution in the proper quantities into the treatment tank.
As to which one is better, that's a big ??? With the electroscan you need to buy salt. I go through a couple 40 pound bags of solar salt a season and spent 60 nights aboard last year. I can buy solar salt anywhere. Lowes sells it for $6.99 a bag. I also spent allot of hours re-engineering their salt feed system so it works reliably.
I do not have any operational time with the new purasan EX, but with the improvements they made over the old unit, it looks pretty Skookum.