I'll see if I can break this down to the most simplistic form. And this, as always, is just my humble opinion.
The P3 vs 510. Endurance, that is it. Bring out all the engineers with their "instruments" you want. It is sturdy had has greater endurance. Period. Now the Kabuki vs nautilus? I used a nautilus from the day they hit the shelves till the day my first Kabuki package arrived at my doorstep. It's THAT MUCH BETTER. Not sure I can even put it in to words here. It is something you will have to try for yourself, or not.
The P3 vs 510. Endurance, that is it. Bring out all the engineers with their "instruments" you want. It is sturdy had has greater endurance. Period. Now the Kabuki vs nautilus? I used a nautilus from the day they hit the shelves till the day my first Kabuki package arrived at my doorstep. It's THAT MUCH BETTER. Not sure I can even put it in to words here. It is something you will have to try for yourself, or not.