It depends what you'll be using it for. I have the 2 arm grapple from WR Long and I don't think I can pick up anymore brush than a single arm like the one Red Horse has.
You do not need two grapple arms. However, I do a lot of work with firewood cut into stove length pieces and I do feel that I can hold more on the grapple. Also, if picking up things like smaller stumps you may be able to get more of a load into the two arm setup. You can also drag two full length trees to a landing area if the stumps are still attached (small trees and be careful because you can bend things).
A single arm grapple will weigh less and is no less capable, so you can lift more with the same loader. You can do just as much with a single arm grapple as you can with a two arm, however there are a few situations where the two arm will get the work done faster and more efficiently.
HOWEVER, if you plan to dig up stumps and trees you will be able to dig better with the narrower grapple, so keep that in mind.
If you are planning on lifting a lot of items that are at the top end of your lift capacity, get the single arm. If you aren't, then the two arm may be better, but the bottom line is, either one will do what you want. There are slight advantages and slight disadvantages to each.
What are your main goals and uses for the new grapple? By the way, whichever one you get, you will absolutely LOVE. :thumbsup: