I've been using the Mares airtrim system since 2006 and I have only praises for the system. Yeah, it is mechanically more complex, but it is very reliable and if it does fail, you have manual options to control the BCD.
What I love about it (in no particular order).
1- The inflate-deflate valve is always in the same place. No searching, you always get your hand on it first time!
2- It really does dump air from your BCD in almost any position! So no more jiggling around to get the air pocket to the deflator hose.
3- For some reason (don't ask me why) the inflator button releases air into the bladder more slowly that any corregated hose inflator I've used so far. And I find this lets me more easily fine tune my buoyancy with small spurts of the inflator.
So that's it! i love it... Never going back unless I have to... tried backplate and wing on single and prefered the airtrim (Using doubles is another stroy; backplates are awesome when doubled up).
Ah yes, I almost forgot 1 downside... The inflator is not in the traditional configuration and in a rescue situation, this could be a concern if the person has no idea about your rig. To reduce the risk, whenever I'm diving with a new buddy, I take a second to show them my system and how it works so if something does occur, there will be no surprises.
It's really a question of preference. Whatever you prefer, it's a reliable well thought out system!
Just my 0.02$
