Not sure I would be comfortable with you doing 90% of your dives solo with such a low number of dives. Especially with "topwater jitters" With so few dives, I could see you going into a situation without realizing it is beyond your limited experience. The spare air is probably worthless in a real emergency. It will give you perhaps 2-3 minutes of air. you can, however, use it for opening different kinds of nuts between dives.
Just my $0.02
Rich
none of my solos are or have ever been deeper that 2at. Everybody has a fear in life and the only way to overcome it is to face it. My top water jitters do not consume me. They are initially distracting and only on the first dive of the day. If they are too distracting I either float topside for a bit or get completely out and try again after a few minutes of relaxing on the kayak. I suffer no jitters on shore dives or high vis. Dives. Only low vis dives. My original dive instructor who will be my AOW instructor as well has been made fully aware of my issue and will help me resolve it with some night dives.
I appreciate the concern. I learn something new every dive and am very comfortable with my gear. I dont fraek out, spaz out and or get the shakes. Chances are you would not even know I had the jitters unless I told you.
Matt
I read this and despite being a passionate advocate on a every diver being able to be self sufficient. It's absolutely unfair to expect a buddy to risk their life for yours! Your disillusioned to rely on either your buddy or even DM to ensure nothing happens to you.
That being said, diving in close proximity to other divers 'with similar underwater practices' adds an extra layer of safety, but 'in my opinion' should never even be factored into your dive plan! ( if they are close by in the event things go wrong its a bonus!!! Not an expectation!!)
Spare Air or what ever similar system you choose I 100% agree with based on diver experience. My personal thought would be 'Open water' divers no way, they should be right next to me and focused on where I am in the water ( I think of it as a well trained dog that is 1 step behind and focuses on maintaining that distance while still enjoying the walk). After reading your posts, I feel you are way ahead of yourself with this idea you some how came across. Don't take this comment as a negative at all!! ( The learning curve that eventually leads some divers in different directions and to perhaps specialize diving a certain environment exclusively, extends dramatically past 25 dives ( I would expect to see at least triple digits, and and the first should at least begin with a 5!

. )
Better still, if you know someone who just got their Driver license, go for a 1 hour drive as their passenger and don't speak. And they have been in a car more than 25 times!!
To surmise, I always dive with a Spare air bottle, but its only to give me the extra 2 minutes or so to figure out what went wrong, and solve the problem. I cave dive so have no option to bolt to the surface, but wish to 'buy alittle time' should I find myself in that situation.
As another diver mentioned, the fact that your asking indicates your not ready! 25 dives in, you should be enjoying this new experience and develop good practices. Example of my pre cave diving prep ( which spanned 3 years on and off). On tropical dives my buddy and I would exchange primary's, share 1 primary, exchange masks, give up 1 fin, swap BC's etc. The practice was always on a shore dive and in less than 10ft of water, so lets not even go there! I've rambled a little, but would feel guilty not commenting should I read your name in the 'Passing' forum
Dive safe.