Make sure you check my earlier post and review the differences between the WM and the Nitroplanes version of the Ultimate 40S.

If you can build ARFs and have some experience with them, the Nitroplanes version is fine. Note that you will need to replace and reinforce a few items.

If you have only built an ARF or two, go for the WM version instead, the directions for the WM version have a semblence of being complete. The Nitroplanes instructions are all but non-existent.

Raidentech and Nitroplanes sell the same version of the Ultimate 40S, WM sells a slightly different version.