A freediving suit makes a huge difference!
I think your question is one that is asked many times and yet it probably never gets a good answer. I hope to try and answer it as best as I can.
The unique properties of a freediving wetsuit is so noticable that, in my opinion, it is like a spiritual awakening
I will never dive in a "scuba wetsuit" again. Even the few times I choose to blow bubbles from a tank, I still dive in my 7mm Picasso Camu. If I were to take up tank diving again, my ultimate suit would be the Picasso Comercial, in either 7mm or 9mm. It gives the best of both worlds. Extreme durability and the warmth that rivals a drysuit, without the superfluous technology. K.I.S.S. is my philosophy on diving.
Picasso, Omer and other freedive equipment companies use Japanese neoprene which is unlike any other product being used in a typical wetsuit. The extreme flexibility and glove like fit make them extremely warm and comfortable to wear. You never have to fight the suit while wearing it. It moves with you, not against you. No zippers and integrated hood provide warmth unparalleled for their price.
Yes they do make a huge difference. They have their drawbacks, but I personally feel that those drawbacks are offset substantially by their advantages.
Hope this helps answer your question.
Safe Diving....