Some may be thinking about trying scooter free diving. It is fun but like SCUBA diving it can be "dangerously" easy that is to say, easy to get into trouble. The gear considerations are important but initially not as important as training and skill development. There is a lot to know and do in scooter free diving. Blackout is a real possibility, even probability depending on how you approach things. In deeper water, undertaking procedures to try to avoid Type II DCS hits is appropriate too. Even hitting things head first on a sit on top scooter is a factor to be concerned about. Being ready for a long list of scenarios from line entanglements to power failures at depth to surfacing with live boats running through the area to dealing with a dead unit at the surface and a good deal more is essential. It can give you a lot of added capability but there is a price!
Taking a good Level II free diving course such as is a good place to start.
F.I.I. Freediving Instructors International - from the beginner to the instructor They teach you a lot of important information essential to higher performance free diving. I have been free diving and studying technique since the early 1970's, despite that I learned a great deal in taking three of FII's courses. I understand they may be preparing a scooter free diving course for folks interested in getting into this.