Probably Safe.
I do not know the ioffer.com site, but I would say that any site using Western Union as their preferred payment method is not to be trusted.
However, this is a quote from the ioffer.com site:
"How do I pay for a purchase?
For your safety, DO NOT complete any transactions outside of iOffer via Western Union or direct bank/wire transfer.
All purchased items are located under My iOffer > Buying > Items Bought.
Click on the Checkout link to pay for a purchase. Use a secure payment method to pay the seller, as sellers are responsible for receiving payments and shipping items."