I have two of the Tractor Supply/Rural King fender mount radios on my open station tractors. I used the radio/speakers that came with them for many years, but have had to change the radios a couple of times over the course of 15 years. I usually just buy a $20 deck off of Amazon (Wal-Mart has some now that seem to work well, too). The enclosures themselves seem to be weatherproof - I've never replaced the speakers. I've even accidentally left the radios in the open position overnight when it has rained and they have functioned the following day. However, as mentioned, I have had to replace them a couple of time, but I suspect that is just as much age/vibration as it is exposure to an occasional shower.
I'm not going to argue that noise-canceling headphones are better in terms of hearing protection. I wear ones like those mentioned when on a vehicle (mower, bulldozer) that is either very loud or doesn't have a radio. I get my hearing tested every year at my workplace and have had no appreciable decline in 20 years, and I average about 300 hours per year on my tractor (bushhogging, mowing/baling hay, etc.). My personal experience has shown me that the sound level is acceptable - your mileage my vary.
One huge advantage (to me) of having the radio mounted on my tractor is that it allows me to use my tractor as a portable jukebox. When working on the farm, I will often use the tractor as a carry-all (as do many others) and when I'm working on the barn, fencing, working on other vehicles, etc., I can leave the radio on and listen without having to wear earbuds or headphones.
I also have a Sirius satellite receiver mounted on my ROPS bar that feeds to my radio. This allows me to mount my portable Sirius receiver on my tractor and listen to satellite radio pretty much anywhere on the farm. I love to listen to college and NFL football games in the fall while I work. I've got the receiver dock in a small plastic tool box that is clamped the ROPS upright, with a couple of holes in the bottom to allow power and data connections to pass through. This has worked for me for about 7 or 8 years and I love my satellite radio.
Good luck with whatever you choose. Take care.