Another of those 'probably not playable' monsters. Not that it'll stop it from getting a LA.
Shield guardians are constructs with 15 HD and bad ability scores, whose abilities are all copyable by low-level spells and all require giving complete control over your character to someone else. If that sentence doesn't prepare you for the -0 LA, I don't know what will.
Yes, fast healing is cute, and spell storing may even have its rare niche in campaigns without Contingencies, but in the end you're a mindless robot slave that's a half-decent meat shield and not much else.