I have made MMF several times and every time it is so sticky and stretchy. I work on a stainless steel table. I roll it out, and I have learned to keep it fairly thick because it is soo stretchy and see through. I use shortening on the table and my hands and powdered sugar dusting before I roll it out. I usually use it the same day I make the fondant, often times within an hour of making it. 

Could that be why it is so sticky and stretchy? Because it hasn't had time to sit?

Also, how do you do striped with fondant because I always roll it out on the table and then it just stretches like crazy and gets all thin in areas and not a consistent stripe. Do you roll it out on parchment paper or something and then apply it to cake? HELP! I just threw away my cake dummy after working on it for two hours and the fondant was just awful!

I also have some Fondx. I tried it before and it is beautiful but dried out in like 3 min. Cracked and everything. Granted, I used cornstarch to roll it out. Getting frustrated over here.....

HELP!

ASometimes I use my MMF right after I make it, and I dont always have problems. I find that when the humidity is high, my fondant is sticky. Try kneading small parts of powdered sugar into it if you can't let it rest. I do think the resting allows the structure to set a bit so maybe try that out too.

I do normally let mine sit as long as I can, but sometimes it has to be used quickly. In this case if kneading in more powder sugar isn't working I roll out on cornstarch...cornstarch seems to dry it up right quick...I have used that many times in a pinch. Also I seem to have this problem when I incorporate corn syrup in my recipe...not sure if you do that...but if you know you need to use it right away I will leave it out...or only add it to the dark colors.

I use MMF exclusively but you definitely need to let it rest before using it, I'll even make mine up to a week before needing it. 

Like the above post suggests, try rolling it out on cornstarch.

Good luck.