Actually, Freedom Fighter's parts are generally more expensive than carriercomps. Freedom Fighter's parts can normally be had relatively quickly.
The machining on the carriercomp parts is superior to the Freedom Fighters.
Top Rails compared. The carriercomp unit has been tumbled to remove sharp edges.
Bolt handles. You can see the knurling on the carriercomp unit is far nicer. The primary benefit is the carriercomp unit uses a steel shaft so that the tip won't wear where the detent engages the notches on the bolt handle.
Hammers compared. Here you can see the OEM and FFT hammers show signs of deformation where the hammer impacts the back of the bolt carrier. The Geissele/carriercomp hammer shows little signage of wear. Or reference, the OEM used hammer has about 12000 rounds on it. The FFT and carriercomp/Geissele hammer have about 2000 rounds on them.
As for the magazine tubes, the carriercomps have a little nicer machining on the threaded portions of the tube. The color finish of the carriercomp matches the M4 a little better.
Bad thing about carriercomp is they take forever to get anything from. I own both carriercomp and FFT parts. So I feel I can provide an honest opinion.