D'oh!
Another tough balance issue from a non-core sourcebook. Oh well, no editor or playtest is perfect!
Yes, we found it unbalanced in conjunction with the Use Magic Device skill. I think Iajitsu Focus would be another great problem example. The one use only ruling helps to balance the spell.
It is a great spell, though, and overall, it's use in most other categories of skills keeps it within reason (although 1st is probably more of a +4, while 3rd would make a better +10 bonus).
What I've seen it useful for, is turning a "difficult" check, in "difficult" circumstances (like combat, where you can't take 10 or 20), into a reasonable check. This has really made players feel better about using skills to accomplish objectives instead of magic or brute force (ie, Disable Device).