Before buying the Bolt I would try to figure out the issues with the 510, which is still a good cycling computer today, since it shouldn’t have problems pairing with the Assiomas via Ant+ or Bluetooth. Maybe it has some connectivity issues, given that you have problems connecting it to your Smartphone.
Have you tried connecting the Assiomas to the Pixel? There should be an app to update the firmware and do some other stuff, so you can see if the connection is stable.
Personally I had a 510 that worked flawlessy until one day it completely died, now I have a Bolt and I’m more than satisfied with it.