I've had these for a year and have worked out great. The only drawback is that you have to have access to the balance plug as well as the regular battery plug, which could normally be accessed from the charge jack. Also, these LifFe batteries hold the charge longer, so a 700 mAh lasts me the whole flying seesion, compared to needing a 1400 mAh MiMh battery that continously self-discharges.
The also charge quite fast, so I can be flexible about choosing which plane to fly at the last minute.