I'm not trying to answer for muscle maker but if assume they are referring to how thin it is.
Myself after years of gso then one time really by mistake like not on purpose, I went with a lab that uses MCT. The normal force I'd use to pull back on the syringe to load it, it just flew back I was like wth?? Same thing with the shots themselves. If it's just a regular shot (no scar tissue issues) it just glides right in. I'm assuming that's what they are referring to.
I like both. I'm actually just about to do a summer run with an MCT lab. I'll see what I think this time around. Been a couple years since I used MCT last.