The MFJ equalized mic (MFJ 299) works very well with the FT-817 and produces great audio reports. For those times when I use the little rig as a base station, a large external speaker and a good base mic make the ft-817 seem very grown-up.
If you plan on getting an MFJ 299, you'll have to either make your own cable or re-wire the enclosed MFJ cable provided for Yaesu radios. Still, it's a great mic!
Don Johnson