Hi Jen. I thought it was funny that you were so excited you forgot to search for reviews. I've been there. Allow me to help you out with HyperOffice, as I am one who chose to use it and am aware of some resources.
I'm a HyperOffice user and am very happen with the decision to use it. You're right that the file sharing is a great feature. It's wonderfully useful. As is the shared calendars feature you mentioned. All-in-all, I love being able to access and share this information from anywhere, as can my clients.
My suggestion is give it a free trial or sit-in on one of their
webinars. Personally, I'm more of a hands-on learner and did the trial. Really, you can do this with any vendor you're considering, and if you have the time, do trials with your top 2 or 3 companies. Nearly all will give you a free trial, usually up to a month!
Also, you'll notice the PCMag review is 3 years old and based one 1 reader review. That makes it a bit irrelevant in my opinion.
You have a great website, BTW.