With the 4* being my second kit building, I found it much easier to build then my Tower Trainer 40. I also found that the instructs that comes with the Sig kits are much more better then the Tower Trainer instructs as well. Just follow the instructs and you will not have any problems. There is also a link on this Forum about some neat modifications with great details you may want to look at as well. I am doing my 4* with the mods. Below is a link to the guys site with all the modifications. He is very easy to email if you have any problems as I have on a few occasions as well.
Modifications by Tom Pierce
GOOD LUCK with the 4*