I think the main advantages of the ironwood would be:
1. Downdraft exhaust for better convection cooking.
2. 500f setpoint. Mine runs 550f when set at 500 (measured with external digital calibrated thermometer). Add a set of grill grates and away you go.
3. 20# pellet hopper.
4. Insulated sides help but a thermal blanket will still be needed in the winter months.
5. Adjustable lower grate.
1. The extra cost. To some it's worth it and some it isn't.
2. Supersmoke mode, if you like a heavier smoke taste.
Keep in mind there are a lot of guys that are struggling with smoking at 225f. Mine keeps it at around 184-195 and it doesn't get to 225. If I set it at 230f it maintains within 10f consistently. 230f and above it keeps it consistent in the range. I'm waiting for a firmware release to address the issue. It seems to be common on all the models that have the d2 controller. I'm happy with mine regardless. Good luck and you can't go wrong either way in my opinion.
Welcome to the forum! I went back in forth for a few weeks trying to decide between these models as well. I ended up purchasing the Ironwood 650 for the reasons @CampWhatnot mentioned above.. I tend to keep things for a while, so I figured I might as well spend more up front and hopefully it would last longer. I know it's minor, but I really like the fact that you can adjust the lower shelf depending on what you are cooking. For me the Ironwood gave me most of the features I wanted in the Timberline, but at a much lower cost. If you have any other questions before you buy, be sure to ask!
I agree with above comments. I wasn’t really looking to upgrade until I read about the features CampWhatNot listed. I was sold and mine is working great. I had my first flare up on a Traeger but it was my fault, I didn’t change the foil. The fire box really shoots out flames at the higher temps.