Great if you want to solo Machamp. They make it much easier even against Bullet Punch + Heavy Slam, Lugia is still really tanky.
Seeing as it's already got 14 or 15 attack if you're going to level it up to 30 you may as well take it to 31.5 / 32 as that's when Extrasensory goes up in damage which will make Lugia's damage output higher.