I'm using Astro to great affect. I'm accessing a shared folder on a network across a VPN. I just set the VPN up in the normal way, and connect to it, and then I'm considered to be a "local" user and I can use Astro. I had to get the IP address of the server I was trying to connect to using the "nslookup" command (google nslookup if you're unsure), and then put my password and username in, and hey presto there was the share drive, easy to copy paste with long press on folder/file, good quick navigation ribbon at top.
I had been trying for hours to get ES File Explorer working, but kept on getting the "Login Failed" message, and a prompt to re-enter my username and password, and I tried changing pretty much everything the internet and I could think of, but to no avail. Astro took me all of 5 minutes to setup.
I don't think you can scan the local network, though, so I'm sure that ES will be better in some circumstances, and if it works straight-off like that then go with it, sounds easy. I'm just putting this out there for anyone who was in my position with the login failed problem.
I didn't think "On Air" was very good - for a start I never got it going over the VPN... when on my home computer it seemed to be just one-way - as in, you could see your phone from your computer, and drop files into your phone, but you couldn't do it the other way around. Personally, I found it to be a bit of a simplistic program, but that's probably what you Mac guys want...nudge nudge ;-) ;-)
