I have both and they are different and yet the same.
Both are smooth, fast, quiet, and very user friendly. Except for the obvious-like the risers-the main difference is in the limbs; the 1 pc has beefier limbs-you can even use it to steady yourself on really challengeing side hilling-never would even think of that with the 3 pc.
Now the bases are covered-3 pc has the extra advantage of limb swapping and packing.
The 1 pc has that classic look and feel of a longbow-you really need both!