Inert gas is usually a mix of argon and co2, which is heavier than oxygen to form a cap of gas over the wine. My only concern is that is does dissipate eventually, and I do use airlocks for bulk aging so that residual CO2 can escape. If I used barrels for bulk aging, I wouldn't need the airlock, as barrels breath.
I just wouldn't know when to replenish the gas blanket since it is not visible. Our liquor store sells the cans of it too, at about $4.00 per can, which they say is good for up to 20 bottles, or I'd guess 4-5 carboys. If you have friends who are welders, you can also get argon in LARGE tanks. Usually Argon/Nitrogen is a good mix to keep a blanket on. You just have to make sure that you've truly degassed. Maybe with an aspirator vac and stones, you could degass enough, the blanket with inert gas and seal it up without the need for a top-up.
To me, it's just easier to top up, and I know I'm protected then.