First question - Older CK35 & KL130 loader (Tier III 2015? and older) or CK3510 & KL4010 loader (Tier VI 2016 & up) because they have slightly different specs.
Second Question - and I'm not trying to be an @$$ - but where are you seeing these unhappy owners at & what type of performance issue are they unhappy with?
I can only find one thread here with 2 posts about the new CK3510 / KL4010 loader & an issue when using pallet forks.
I ask because generally speaking if you find someone unhappy with the tractor performance they are asking it to do more that it's capable of and probably should have bought a larger tractor to begin with and I just want to make sure that's not the case here.
For example - My Father and I "Co-Own" our tractor (Well he paid for it but I end up running it most of the time LOL). I know we were slightly "disappointed" when we discovered it wouldn't lift *all* round bales of hay (dry 4x4 No problem, green 5X5 or larger - forget it) but . . .
1) We didn't think about that when we bought it because we weren't moving round bales then.
2) We don't move that many round bales now anyway (maybe a dozen a winter) and it's only for place to place transport not stacking / unstacking so we're eventually going to make a 3pt hay spear.
If those were considerations when we bought it, we would have stepped up to a DK40 (and almost did anyway).
All in all we have done quite a bit of loader work including dirt moving (rebuilding a pond and excavating for retaining walls), spreading asphalt millings, and LOTS of
grapple work and so far I have not once been disappointed in what the tractor / loader can accomplish - I just have to remember to work inside it's capabilities. As my father is fond of reminding me, it's a 35hp farm tractor not a D9 dozer.