never gave it a thought but after dwelling on it abit I don't think there are many similarities other than they both go under the water and both "should" have a buddy. generally - fins, masks, wetsuits, and weight belts used for freediving are different than for scuba. Techniques like finning, equalizing, leaving the surface are different between the two. Amount of time you can spend under the water is obviously different, and what it takes to get bent is different, different cautions have to be taken. and then there's the zen of freediving.. if you get into that sort of thing... And another thing.. there is no comparrison of the fluidity a freediver experiences in the water compared to an encumbered scuba diver. there's the equipment cost, certifications, etc. etc. too.. No.. not to many similarities that I can see.