I seriously recommend it. I put mine over my roadcrafter, and i stopped noticing that i was wearing it within 10 miles. Now "clip in!" is a reflex just like "buckle up!" is in the car.
1) I trust the tether a lot more than someone else's (or my own for that matter) software
2) No battery to forget to charge
3) Uses cheap CO2 canisters making it and easy to re-arm. Many airbags have to be sent back to the manufacturer after a deployment and are quite expensive to re-arm.
hit-air does all this too; i liked being able to bring my own back protector and the improved ventilation of the bag-only system. The helite turtle doesn't breathe quite as well.