I had my 2nd device for 11.5 years. From a user point of view, there doesn't seem to be a lot of difference but probably it's ability to recover pace is improved.
And yes, the data within is readable and the device can be reprogrammed externally as well. They once changed my defibrillation trigger point from 180 bpm to 190 bpm. Also, they can vary the power of the little impulses for pacing. They did this once on mine trying to make them small enough not to stimulate my diaphragm muscle yet big enough to be sure my heart reacts to them.
I was very worried when a relative got their pacemaker/defrib combo unit.
After looking how easy it was to install and how the maintainance/checkup involved waving a wand over the chest, I would never hesitate to get one for myself if I needed it.