Ive not tried the adder but ive popped countless NPC ones using variations of sidewinder, eagle and viper. As mentioned above they are the camper van of space.
I started out with sidewinder and my freagle. I really like both of them, I bounty hunted and missioned both until I could afford to outfit both.
There is a post somewhere about the eagle, giving some advice about outfitting. The idea is you swap the shield with the cargo hold below it then you can install an 8ton cargo hold, choosing to keep your other cargo or install something else and keep your shield. Which means you can take some cargo missions if you find you need to pay some bounties
Although with the eagle the armour is very very weak once your shield has gone you are going to take a lot of damage very quickly. So fly in a way where they can't hit you, or use your pips and hold them at distance till you have full shield and then get in close and nail them. Cobras are like a barn door when you get inside them can't miss you can even choose where you want to hit them FSD, Cockpit etc. Vipers with a good pilot are a lot harder to take down.
Don't go after the high value assassination missions in your sidewinder though ......
I have actually gone back to my sidewinder as I'm saving cash to upgrade my Viper with high class equipment. I don't plan to trade my way up just use missions and bounty hunting. Im not using a fuel scoop in my viper as I have a interdictor in the place. So its more economical fuel wise to hunt in my eagle and my sidewinder (Also the replacement costs are cheaper as accidents do happen).
I would stick with your eagle until you can afford to outfit a viper, or just buy it keep it somewhere and add bits and pieces gradually to it. The eagle is cheap to repair, fuel and insure.