I have a RS discone (whichever model it was they sold in 1995) that has been on my roof for 11 years with nary a problem. It mostly sees duty on the scanner and works fine. I have also used it to transmit on 2 meters, 222 mhz, and 440 mhz. When my son got interested in 1998 I got him the Diamond. It's been up on the roof on the other end of the house since then. Both work the same as far as I can tell.
Keep in mind that a discone antenna has "unity gain." That is, it has no gain, and that fact can be a disadvantage. The advantage to it is that is very broadband. Of course, its unity gain characteristics make it great for monitoring aircraft.
Lee, K3GI