A decent quality bolt on toothbar will actually re enforce your FEL cutting edge as the teeth are usually welded onto (approximately) a 3/8 or 1/2" flat bar that is about 3" wide.
Then for penetration they generally space the teeth about 6-10" apart.
That is about as close as can be to excavator style configuration.
The piranha style consists of much closer spaced blunter shaped (but sharp) teeth that would deflect on much smaller and closer stones.
I'd suggest Piranha would be superior for removing overgrowth than a spaced tooth bar while the spaced tooth bar better for real time digging.
Piranha would also be better for 'rakeing' type operations with the 'teeth' being closer but would also drag more topsoil than a spaced one would.
By design the Piranha would cut small roots as you'd scoop away overgrowth.
Both have their advantages and disadvantages.
Add to the equation that the 'bolt on' has replaceable teeth.
INMO for serious digging in virgin stone imbedded soil the spaced toothbar will excel while the Piranha would excel in previously prepared soil situations that have little or no stones.
Just look at the teeth on an excavator and you will understand, or a tracked FEL.
For sand and crushed they use nothing but to dig the use well spaced teeth!