Integrator 3 will work with Kayako Fusion v4.5 as well as Joomla 3.2 - I have tested these and confirmed it on a number of installations. Users are indeed synchronized across Joomla and Kayako. Each system independently maintains their users, and when a change is made on one system, the update is carried over to the other. if the user doesn't exist in the other system yet, I3 will create the user there (if set to do so). When users log in, they only have to authenticate against one of the systems, and once authenticated they are logged in across both.
So long as the default user registration group in Fusion has permission to create a ticket (ie they don't need to be added to a custom SLA or something) then it should work.
I am using Joomla 2.5 / Fusion 4.5 / WHMCS 5.2 with I3, and when a user registers they are added to all three systems and can open tickets once registered.
The only thing in Joomla 3.2 is the two factor login can't be made to work with I3, but aside from that it will work for you. Users aren't 'synced' like they would be in JFusion, but they are maintained as changes are made, with the result that the accounts are kept in sync.
While we don't offer a trial product, we do offer a leased product, which greatly reduces the initial investment; should you decide that it meets your needs you can upgrade the product to a purchased license and we'll apply the initial lease payment + setup fee towards the purchased price - just ask us to upgrade you within 30 days and we'll put the order in.
You should note that with Fusion there are several core file changes that need to be made as Fusion has implemented a number of changes over the course of the past few years with version 4 including CSRF protection on log in etc. The changes that are needed are documented at www.gohigheris.com/documentation/integrator-3... we are working on bring those up to date in our new documentation area.