Well, from the research I did on HCG 500iu/day for 2day/week is not considered heavy duty or I wouldn't have done it myself. There's a ton of info out there about it, so you should do the research til you're sure you're satisfied as to whether it's safe or not.
Here's a good all-viewpoints article on HCG...
http://www.rippedcanadians.ca/articles/hcg.html
Anabolics 2000 says "The usual protocal is to inject 1500-3000 iu every (4th-5th) day for a duration usually no longer than 2-3 weeks . If used for to long or at too high of a dose the drug may actually function to desensitize the Leydig's cells to Lutenizing Hormone , futher hindering a return to homeostasis!" This may be where the 3 week limit comes from but this is referring to PCT pre-Clomid. That seemed like a TON to me, which is why I preferred the once week thing. Besides, like I said, it helped prevent the shrinkage AND the pain to do it that way, rather than holding off til the end.
I'd like to learn more about whether the 2days/week thing is excessive or not though, so if anybody's got info that that's not good please post it!!