Looks like they follow the fund's 13F filings, which is unreliable and misleading at best. Funds with over 100MM assets must file this report quarterly, and it only contains long positions - not shorts, and some other traded instruments, so you're not getting a complete picture of what the fund's actual exposure is. Worse yet, some funds purge their book before the end of the quarter in order to only report what they want to report. Lastly, these reports are filed a month or more after the quarter end so the report may or may not reflect what the fund currently owns. The end result is you end up with very little insight into what the fund actually owns/is doing TODAY.
And let's not get started on the underperformance of many, many, many hedge funds in the past few years relative to the S&P...
So if you want to stock pick, go ahead and stock pick - but "shadowing" a hedge fund using just this data is like wearing a blindfold while running a marathon.