None at all! Unless it were actively and carefully manipulated to undo your specific RNG (i.e. were not independent) which is absurd, you can use it as one source no problem.
Imagine you have six sources of entropy and they all suck except the third one, which is independent and works. All the others are actively working together to manipulate your result.
Then xor'ing the bits
a xor b xor c xor d xor e xor f
can be rearranged to
(a xor b xor d xor e xor f) xor c
and it is the exact same expression. (xor is commutative.)
But now it's clear that C acts like a "one time pad" on the whole rest of the expression, making it truly random.
Of course, if it's not independent, for example if A is reading C and set equal to it, then this argument does not apply.
But it is highly unlikely that this beacon could be specifically manipulated to target weakening a single specific user of it. For one thing it couldn't be done with more than one person at a time.
So we can ignore the possibility that it is not independent of your other sources of entropy.
Go ahead, go wild including it.
(I say this even though I place the likelihood that this beacon is backdoored and predictable to the government, at 200:1 in favor.)
Two techniques you can use:
1. Mix with other sources of entropy such as number of milliseconds on the system clock. Doesn't matter if they're weak - do this yourself.
2. Draw from the beacon continuously, discarding values when you don't need thsm. Don't just draw when you need it.
These two techniques will make it almost impossible to reconstruct the random numbers, even if the sequence were predictable by someone.
By contrast, only using this beacon mixed with a backdoored rng, without xoring by some function of the system clock yourself, and only drawing the number of bits you need and doing so every time you need them, will make your solution considerably easier to bruteforce if your rng is backdoored.
Imagine you have six sources of entropy and they all suck except the third one, which is independent and works. All the others are actively working together to manipulate your result.
Then xor'ing the bits
a xor b xor c xor d xor e xor f
can be rearranged to
(a xor b xor d xor e xor f) xor c
and it is the exact same expression. (xor is commutative.)
But now it's clear that C acts like a "one time pad" on the whole rest of the expression, making it truly random.
Of course, if it's not independent, for example if A is reading C and set equal to it, then this argument does not apply.
But it is highly unlikely that this beacon could be specifically manipulated to target weakening a single specific user of it. For one thing it couldn't be done with more than one person at a time.
So we can ignore the possibility that it is not independent of your other sources of entropy.
Go ahead, go wild including it.
(I say this even though I place the likelihood that this beacon is backdoored and predictable to the government, at 200:1 in favor.)
Two techniques you can use:
1. Mix with other sources of entropy such as number of milliseconds on the system clock. Doesn't matter if they're weak - do this yourself.
2. Draw from the beacon continuously, discarding values when you don't need thsm. Don't just draw when you need it.
These two techniques will make it almost impossible to reconstruct the random numbers, even if the sequence were predictable by someone.
By contrast, only using this beacon mixed with a backdoored rng, without xoring by some function of the system clock yourself, and only drawing the number of bits you need and doing so every time you need them, will make your solution considerably easier to bruteforce if your rng is backdoored.