No registration required! (Why?)

Concerning CME PC SPAN software

Hello everyone,
I'm new so please be patient with me)
Can anyone please identify pros and cons of PC SPAN software?
Are there equal software programs like it that would be able to calculate margins?
If there are, can you please let me know what they are?
I've been looking for reviews from traders regarding SPAN but have no success in finding any.
Before committing to a pricey PC span, I want to make sure it is indeed the best option on the market of futures and options at the moment.