Yes, typically external speaker jacks on radios are 3.5 mm and external speakers use 3.5 mm plugs.
Does it need an external power supply? I wonder if the wall wart I use on my mfj949E will work on it...
Should be plug and play then. Read the manual before you start messing with it. Just what I would do. They most likely will have some settings to help get you started. Again if you buy it for the price it's worth as long as it works. If you can verify this before purchasing it then I would grab it up. If not someone most likely will unless it's a close friend or something. Keep us updated.
Will do.