Hi Tom.....congrats on your new tractor. I also just bought a new 2520 last fall, and was somewhat confused about the independent lift vs mechanical lift deal. One salesman, (at a dealership where I didn't end up buying) was very adamant that the independent lift was the only way to go. He didn't even ask what I wanted to do with the tractor, just insisted that I needed it. Probably because it would have resulted in it being a higher dollar sale.
Glad I didn't listen to him. Unless you are going to really need, or see the need down the road, to have the ability operate the 3pth totally independent from the mower lifting action, you don't need it.
If you do have the independent lift, and want to have full control of your loader and deck at the same time, you have to buy the add on remote SCV outlet which gives you another 2 hydraulic outlets so you can keep all the loader lines and lift cylinder all connected. In addition you will need to buy the SCV control valve, so you can switch the fluid flow between the loader ports and the deck cylinder. If you don't go this route, you will have to manually switch out 2 of the lines from the loader circuit to operate the mower lift, and back again when you want full control of the loader again.
As runner has said, it seems that the independent lift will leak down, which to me would seem to be a real PITA especially after paying a good buck for it.
One thing you should consider though is that when your mower is off, and you are using another implement, the mowers lift arms will also go up and down with the 3pth. The only time at the moment when my deck is off, I have my front blade and ballast box on the rear. In order to keep the deck lift arms up, I bought the JD deck lockup kit. The kit is a little pricey (in my case in Canada it was $175) considering what it is, just a couple of brackets and adjustable chains, but it works. Some guys just use bungee cords or big zip ties, to do the job, but I'm happy with the JD kit despite the cost.
I know there are some cases where one would want independent control of the 3PTH and the mower deck, (like if you want to run your rear tiller and still keep the deck on) but in most cases I would expect if I had an implement on the 3pth, I would take the mower deck offl. The drive over decks go on and off in a couple of minutes. Then I can just hook up the lockup kit chains and the mower deck arms are out of the way, and I have full control of the 3PTH.
REV