I would get both the thumb and the grapple, but I assure you in no uncertain terms that you will not regret a grapple if you have trees and stumps/roots to move around out in the woods. The picture below is a 60' EA Wicked Grapple and it has only been off the machine twice since I bought the tractor and grapple. Once I put the regular bucket on to move 20 yards of mulch this past spring, and the other time was... was when the tractor was new and I had not installed the grapple yet.
I thought I would be chaining and dragging logs around, but that requires getting off the tractor. A grapple is just a huge convenience and is very efficient and effective. (Plus you can run around with the cutter to get two jobs done at once.)
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As to the ECU, I would ask the dealer to triple check with Mahindra on the version of the ECU program they are currently using. I believe there was one 2538 owner up north who was having a little bit of a rough idle and warm up after a recent ECU flash. I guarantee Mahindra corporate heard about that and likely tightened up the take points. They do seem to be tweaking the programming a bit on these new mCRD engines and maybe they went a little too far for the northern climates on that particular one.
I honestly don't know if my "newer tune" from late summer was the latest one or not, but it is now running in beast mode down here in Houston which rarely drops below 40 degrees during winter operation. Programming is easy to update, and if your dealer is close enough you could ask them to swing out with their laptop to do an update if there were any performance mods available down the road. My guy is close enough I can swing by with the trailer when heading out to property and the can just plug in the laptop and be off to the races in about 10 mins.
Check out this video of Ted using a smaller tractor to handle some chores around the house. Fast forward to eight minutes if you want to skip the discussion.
Good luck with your decisions!