The SIG 4-Star kits are certainly excellent kits and easy to build. Whether they are "the best" or not is a matter of debate. If you follow the instructions, you should not have any difficulty.

The 4 star is easy to cover because there are very few rounded areas, it's pretty much straight stuff accept the "turtle deck".

They come with decent hardware and you are not required to cut out any parts. You may be required to "fine tune" some parts to get the proper fit. You will also need to cut sticks to length.

I don't believe that they give measurements in metric.

I have not built a "Something Extra" but have the 4 * 60 and highly recommend it. It can do faily aerobatic yet is easy to fly and land too. I prefer the 4* 60 over the 40 due to it's size and it comes designed for 1 servo per aileron.

Kent