Investing in RTBs are considered risk free because it is guaranteed by the Philippine Government. When you invest in any government bond, you can rest assured that you will get your principal and interests in a timely manner.
However, government bonds still pose some risks like inflation risk and opportunity cost. Inflation risk is the risk that an investment will not grow fast enough to offset the loss in purchasing power, while opportunity cost risk is the risk of missing a chance to earn a higher return by investing in a particular security.
Make sure that you understand the product and all the risks involved before investing, and determine independently that the product is suitable for you.