Hi, while its not easy to get the SFH485P, i got the SFH485 (20° version) and filled it flat (but im not in UK).
Freetrack should work ok with red leds, but i guess the 2.5V version will need very strong source (9-12V), and will cast red visible light on your monitor. Not sure how it will work in bright daylight since you won't be able to use VIS filter, but maybe it will with good settings on webcam.
So while i think most ir LEDs are superior for freetrack use, it should work.
EDIT:
Here are some problems solving with visible light LEDs.