The gun is not really that overpowered, it's just to do with where you put it. For example, if you put it in some random easy to reach corridor to let anyone take it constantly, then yes, it will be over powered, but If lets say you make a map with a large room in the middle, and small tunnels going around it, and make the room pretty tall, at the top you could put the egon on some platform, to which you would have to complete like a series of box jumps or ladder climbs to get to, by which time you could already be dead before you get it. That would be a lot less overpowered since it would be quite hard to get to it.
Also there is the issue of the small ammo usage for it, but why add ammo for this gun into your map? If you don't like one player hoarding this gun and constantly raping everyone cause he has so much ammo, don't add any. I'm pretty sure the standard gun has 20 ammo alone, and that's maybe 2-4 kills?