Salasis's page

If you are adventuring in the underdark invisibility won't be that helpful at any level. If anywhere else invisibility only loses it's luster against certain monsters. I've played an arcane trickster to level 17 and used invisibility the whole way. Every now and then you will run into tremor sense or See Invisibility but their isn't really a level cap on it.
It does only provide a +20 to sneak so someone with ranks in perception could possibly still detect you.

so that makes me wonder...When would transformation be effective. Unless your out of spells at which point i would pick teleporting away over slogging into melee.

Thank you very much. I appreciate the clarification.

Does the antimagic field cancel the trnasformation?