Once the firmware was flashed with an incorrect firmware then your friend voided the products warranty and even if you flashed it back to its original firmware then Lite-on would still know if it needed to be returned.
Other than that the drive is a good one and should be fine for sometime to come.
If the drive has only been used once or twice every couple of days then it will be fine but if it has been hammered then stay clear.
If the drive has only been used for -R then this should not cause any problem's but it could be worth testing with a +R just to easy your fears.
When all is said and done if the drive is only 6 months old then there should not be any problems, try asking your mate if you can trail it for two weeks before you part with any cash but to be honest these drives are that cheap now it might just be better to go and but a new one.