They are also as safe as any PP->BTC transaction (i.e. not safe at all).
Paypal does not allow trading of digital currencies. If you are caught, they will freeze your account and any assets on your paypal balance.
Other than that, a typical paypal to bitcoin transaction puts the person receiving the paypal currency at highest risk, since the buyer can dispute it at any time.
This site appears to use some type of escrow, so i'll have to read more into it.
When reading the how "How it Works" section, I found these two important notes.
Seller uses the link provided to perform PayPal funds transfer directly to the correspondent Buyer. Seller is provided with a pregenerated and tamper protected transaction template link and only able to confirm the ongoing payment. Resulting Paypal transaction does not disclose deal details nor it reveals a BitCoin exchange deal. It only says Order#XXXXX.
Credit card transactions are vulnerable for chargebacks. PayPal transfer operation fuded by CC transaction is automatically being reversed once chargeback notification comes from cardholder issuing bank.
So, if the PP transaction is as discrete as the description above, you shouldn't have to worry about your PP account being frozen. As always, beware the CC chargeback, read more on their FAQ