To start with, all the cars will slide out under braking if they are not set up properly. Just .5mm difference in the length of the shocks can cause this.
I have not had my 705 long but the running it has got has been good and no sign of being on the edge as Mitch179 mentioned. I guess the guy driving it that day just didnt have it set up correct.
As for small/medium sized tracks - thats what I generally race on and this car works well. Again, it comes down to set up and what type of tracks you hvae been used to. In America most people are used to fast flowing tracks and know how to set the car up best for them. In the UK/Ireland we use many different track types every other week and we are most adapt at setting a car up for all track types
Get everything set up perfect (which is easier with a Serpent) and dont have your brakes locking up and you will have one really fast car. On the other hand rush the set up and have a really twitchy looking and feeling car. Its that simple.