It would be helpful if people identified the diving environment they're coming from ... because pros and cons do vary depending on where you're diving. I'll give you my reasons for going sidemount, how I generally dive them, what I like about it, and what I don't.
I'm a 60-year old man ... diving mostly non-overhead in a cold water environment (drysuit, heavy undergarment). I enjoy solo diving, and occasionally go beyond recreational depths ... sometimes well beyond them. I occasionally cave dive, and even less occasionally go inside of wrecks ... mostly those placed down as artificial reefs, since we have several of those within reasonable driving distance to where I live.
Now, what I like ... sidemount gives me easier options for solo diving. As a photographer, I used to dive single or manifolded doubles while slinging an AL40. Slinging a 40 while carrying a largish photography setup tends to be a bit of a cluster. Sidemount cleaned that up quite a bit. I also like the fact that with sidemount, my redundancy is independent of each other. Being 60, I'm not as limber as I used to be. My joints, particularly a left shoulder that was injured years back and never ever came back as flexible as it once was, made valve shutdowns less smooth than they should be. While I could do them, I was never comfortable with the limitations of my body. Sidemount removed those limitations because I can now easily reach both valves ... and the fact that I can see them doesn't suck either. I love the feeling of sidemount. As a photographer, I find I can more easily position my body however I like for the optimal shot without fighting the "keel" that a backmounted cylinder often tries to become. Sidemount just makes the whole diving experience feel more natural, rather than like an adaptation you have to get used to.
Now, what I don't like ... people talk about the freedom of getting in the water without the weight of your tanks. Well, guess what ... you still have to get your tanks to and from the water. This can involve multiple trips ... and since I predominantly shore dive, often in places where the water is well downhill from where I park my car, this can often be more difficult than just putting on your tank(s) backmount and walking down once. And the return trip is uphill, which can often be even more work getting your tanks back to the car. Then there's the additional time of clipping the tanks on once you're in the water. And for shore diving, I specifically don't like the notion of wading into the water without the option of having a reg in my mouth until I get to where I dropped my tanks, clip the left one in place, and turn it on. In certain conditions, I prefer to be able to put a reg in my mouth before my feet ever hit the water ... just in case. For boat dives, getting on or off the boat requires a choice ... tanks on or off. If tanks on, you have to clip in and route your drysuit and BCD hoses after getting into the BCD ... which is not as easy as it is in backmount. If tanks off, you have to giant stride in without your tanks, find them clipped to a line, and get into them before you begin the dive. Again, depending on conditions, this can be much more effort than backmount. Getting back onto the boat you're faced with the same choices ... climb the ladder with your tanks on or spend some time and effort removing them before getting back on the boat. Neither option offers any overall advantage over backmount, just different trade-offs. Add to that the fact that boat gates are not designed with sidemount in mind ... meaning they're often too narrow for a standard giant stride with sidemount tanks on, so you have to angle through and do a "modified" giant stride while standing somewhat sideways. It's not difficult, but it does take a bit of getting used to. And finally ... something I've yet to hear anyone else bring up ... both of my drysuits are showing definite signs of wear under the armpits, where they rub against the tank valves and regs. Drysuits aren't designed for sidemount, and don't have the reinforcement there that they have in places where standard backmount tends to produce wear. My Santi suit has developed an armpit leak that's just giving me fits trying to find. I never had a leak there until I started diving sidemount ... and when the water temp's in the 40's, a leak in the drysuit isn't any fun at all.
So those are my sidemount pro's and con's. I'm sure they don't apply to everybody ... just as I'm sure some of the blanket statements I've read so far in this thread don't apply to me ...
... Bob (Grateful Diver)
