DS-6610B ISL Trunking License Purchase Options and Disadvantages of Without ISL Trunking

Hi everyone,

We plan to connect two DS-6610B.

I am new to fibre channel switch. 
From what I have researched and understood, even without ISL trunk, it is still possible to connect them, but without the load balancing.
I am evaluating the cost and necessity of ISL trunk in our environment. 
I would like to know if Dell offers the option of purchasing an ISL trunking license alone? Or can We only purchase the Enterprise Package?

And we want to know, besides bandwidth and failover time, the disadvantages of without ISL trunk?

Thanks!