ILF limbs fit ILF risers, that is the big deal i guess. ANY limbs smack on ANY riser, biggest hurdle is having a string of the correct length.
Invented by Earl Hoyt (I think) this limb to riser attachment is now industry std. on quality FITA/ olympic style bows. Production volumes are vast, as are the available development resources. Hence, very high performance are available. Tradeoffs between opposing qualities still there off course.
You get good ILF limbs, cheap ILF limbs, expensive ILF limbs, probably bad ILF limbs (though havent seen any yet), short, medium and long.
On a 25" riser long ones make a 72" bow, and short a 68" bow. Shorts on a 14" riser should make a 57" bow.
Generally they are marked XX# on the 25 and 23" risers, usually gain about a # per " you go down in lenght.
ILFs are mostly recurves but longbow limbs are to be had.
The real beauty as said is (cross brand) interchangeability,
2 risers and 2 sets of limbs make 4 different bows. 3 risers and 3 sets of limbs are 9 bows!.
Availability of low cost or used proven and high quality limbs is another.
K