Questions..
Have you been trained to use one?
Have you seen an instructor demo the skill, live or YouTube?
Relatively speaking, the smaller the smb the less you'll exhale to inflate. But, it's more of a transfer of bouyancy, from your lungs to the smb. This takes practice. Here's a video of a proper smb deployment....
SCUBA: SMB Deployment - YouTube
Each smb is a tool and is used for a specific purpose. For training and general use I like the HOG 36" and the Halcyon 36". A simple 50' spool and a SS double ender and that's a simple, useful set up. Now, rigging that set up is another chapter.
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