bartholomeus, if you are in Miami I would STRONGLY encourage you to NOT get a Bel 980 or any of the earlier Vector series. They are EXTREMELY susceptible to heat, and won't work when hot.
The X50 is also prone to heat, but it is not black, so it tends to not get as hot. I have owned all three of these (Bel 980, Pro 78, and X50).
You need to figure what your normal threat is. Where I live it's 75-80% K band, so the X50 is better for me. If your main threat is Ka band I would say buy the Pro 78, it is just about equal, and is built like a tank inside. Here's a link to a private review of the Pro 78 complete with pictures of the inside of the unit (GOLD plated contacts!!!):
MEM-TEK's Whistler Pro78 Review