As @assylias said, if the company goes under you get nothing. So bond investing is not risk-free.
Further, you won't get a 6.25% return. That's the coupon rate, based on the face value of the bond. Interest rates today are much lower than that, and the price you pay for a bond reflects current interest rates. For example, if a long-term bond paid 10% of its face value and interest rates went down to 5%, you'd have to pay $2000 for a bond with a face value of $1000 (oversimplified, see below). That's how the bond market works: prices adjust to keep the interest payments in line with current interest rates.
Here's the catch: regardless of how much you pay for a bond, when it matures you get its face value. If you paid more than face value for the bond, which is the case for just about any bond purchase today, you eat the difference. That's the oversimplification in the previous paragraph: the price also depends on the time to maturity. The longer the remaining time, the closer the price will be to the value dictated by interest rates; the shorter the remaining time, the closer it will be to the face value.
One further, but minor, complication: when you buy a bond, in addition to the purchase price you also pay pro rata interest to the seller. Bond interest is typically paid every six months, which is why the coupon payment for your example is $312.50; that's 6.25% annual interest, divided by two because there are two interest payments each year. If you bought the bond on July 15, you'd be half way through the six month interest period, so you'd pay the seller $156.25 in interest. You'll get it back in January, when you get the $312.50 interest from the bond issuer.
So what you get back on a bond investment if you hold it to maturity is interest based on the face amount of the bond and, at maturity, repayment of the face amount. Look at what the bond will cost you, and decide whether it's an appropriate investment.