Jazzy:
These are quite different from the FretFX markers. The FretFX are actual, individual LEDs. The Fretoptix is a single LED that mounts behind the headstock and has a fiber-optic line running down the side of the guitar. If you go to their website and look CLOSELY, (very closely, they appear to be trying to hide this part of their product), you will see that these require a fiber optic line running from behind the headstock to the front in a big loop (likely in the way of the tuners) and then runs down the side. I would suspect the side markers are not as big or bright as the actual LEDS. Also, these won't work on a Strat which doesn't have 24 frets.
As is almost always the case, you get what you pay for.
Hope you have a healthy, happy, and musical New Year.
Bill, tgo