I will answer these questions from what I have learned so far working with the Parrot Mambo quadcopter in Matlab/Simulink:
1. The sampling time of the communication is slower because it cannot be processed in one sample period of the embedded computer (Mambo). If TCP is being used, as a communication protocol, some processing is being done to deal with the received packets, such as checking for errors. Furthermore, this communication protocol, which was designed aiming reliability, guarantees that the data is delivered in a certain order, so you might have a huge delay during the experiment. Increasing communication frequency will not make it necessary faster. On the other hand, if you are using UDP, which is a connectionless protocol, you will have a faster transmission, but with no guarantees of delivery and errors checks, the data is being sent and the sender does not bother if it is being received or not, or even how it is being received. Using UDP the maximum communication rate I could get with no errors from SImulink was 100Hz and I have not used TCP/IP so far. You could read more about the differences between TCP and UDP in the following links:
2. The motor speed varies when you are sending them through the PC because you will not, and I would also say that you can not, receive a data packet per Mambo-sampling time. Consequently when the input value is not defined it goes to zero. This means that the output of the motors will be weaker, as you have as an input a ¨modulated¨ signal. From the TCP/IP receive block:
¨The Data port outputs the received data as a [Nx1] array. The Status port outputs 0 when the available data size is less than the Data size parameter.¨
3. I believe that in the tutorial they make this suggestion only as a start point for working and getting acquainted with the development cycle using the Mambo quadcopter. I strongly believe that it is not possible to control the pose by sending motor inputs from the PC using this system. Only slower dynamics can be done this manner, such as height and position, for example.
I hope my answer helps you somehow.