It's pretty annoying when you've personally set aside two hours and then learn your partner only set aside one. It will take at least two hours. It's a forum!
Your mind will be elsewhere and you'll feel rushed to get back to the office. Moreover, you'll be unfair to the member you're meeting.
It's kind of impersonal when your assistant calls. Also, assistants are often accustomed to running interference for their all-powerful boss, so they can sometimes come across as officious. And you will almost certainly come across as self-important....not a great start for what should be a great MicroForum.
Believe it or not, this can be a source of embarrassment to some members. Just plan on splitting the bill down the middle.