I have been using the red version of these standard base S-11 Festival LEDs with spectacular success. Pre-fogged testing with Ilford MGIV, both FB and RC, shows no safelight-induced fogging out to at least 60 minutes.
The only caveat is that none of the LEDs I tried emitted absolutely pure light. In addition to the main peak centering on the design wavelength (635nm in this case), the S-11s were also generating small blue and green spikes. I could see these clearly by simply observing the light reflected in a standard CD disc. These spikes did add to the paper fog levels after a few minutes exposure.
I solved the problem by enclosing the bulbs under a single layer of Rubylith. This acted as a poor man's low-pass filter, effectively blocking the higher frequency spikes while passing almost all of the lower frequency red light.
The blue and green disappeared from the CD, and the safe exposure times for the papers jumped to the 60+ minute mark. (I stopped the test at that point, so I don't know how much further it might have been able to go.)
I eventually hacked up a DIY bank of six of these bulbs to create a relatively bright working environment.