I don't know that particular unit. It took me a while to stop noticing that the pacemaker was running. It was a new heart rate for daily life (about 15 bpm higher resting) and it was a weird feeling.

I also had to have some of the settings tweaked a few times. The biggest impact was from the setting which raised the rate when I stood up and started moving. It was on the default which was for a 80 year old in the hospital so it had a very slow response. I'm in my 40's so it needed to react much faster when I would stand and start moving. Once that was tuned somewhat almost all of the poor out of breath feelings when I would stand and move vanished.

As to "feeling it fire" - not directly. It's just my heart beating. The difference is when and how much. I also had a long time worrying about it. I (and my wife) did some therapy to help me understand the changes to myself and to address fears. That helped a ton.