In most ways, it should be a strength. Your sword will be more durable and less subject to external factors both physical and magical. If it's up against a non-magical weapon, your sword should win every time. But if something does manage to damage your sword, it will be hard to repair. Otherwise, assuming these metals aren't magically potent, the end result should be similar to a normal if extremely hardy sword.

[ Even if that pulsing metal begs a second look... ]

Most importantly, rune magic is tied closely to its caster. None but I can remove the spells on your sword. But if I cease to exist, the magic will be undone and the sword will revert back to its pre-magic state.