Colliam7:I will stay completely out of the 'should you', 'should you not' arm of this thread. In a separate (very long-running) thread on 'most regretted' equipment purchases, a SpareAir was an often cited item. That is not a judgement, merely exposition of the experiences of a number of other SB folks. 'Small pony bottles' (less than 19cf) was another often regretted purchase. My opinion, FWIW, is to go with a pony. And, I would consider going with a AL40 pony, simply for future versatility (even resale value if you decide to move in other directions). I dive one slung under my left arm - hardly even notice it in the water. I feel more comfortable with it at 120' than I would with a 19cf.
Agree completely. Get an AL 40cf pony, sling it from two D-rings like shown in a couple of photos in this thread and I guarantee you will not even notice it when you are diving. You'll have a substantial amount of air no matter what depth you dive, and you'll have a nice stage bottle when you're ready to move on past recreational diving.