I also have a 2520, and also the "lock-up kit". As "Prosperity" says, it does seem expensive, for what you get.......a couple of brackets and 2 adjustable chains. The kit is also intended to lock up the deck if you want, so the 3pth is then free to operate independently. If you get one, don't leave the chains on unattached. Mine actually threaded one of the adjuster buckles all the way out, from the vibrations I guess, and I lost it. Luckily I noticed it missing, and was able to find it again. Now I take them off if I'm not going to use them. I pretty much just use them in the winter, when the deck is off, and the front blade on.
When I ordered mine, I really thought it would be some sort of mechanical locking mechanism that you could engage right from the tractor seat, but no, just brackets and chains.
The kit does the job alright, but since I am not the "build it yourself" kind of guy, I really didn't have any choice, other than to go with the "red neck" kind of solutions........tie wraps/bungee cords, or take the arms completely off, which I didn't want to do.
Seems like a lot of money, but I sure couldn't have had something fabricated for any less I'm sure.