They work fine but they generally dont compete in light output with the better lamps. I have a Current fixture and did buy some of the ATI and Geissman lamps to try. Just for an example, the Geissman actinic is visibly brighter than the Current Actinic.
Personally, when it comes to replacing lamps or swapping colors I think it is worth spending the extra 4 or 5 dollars on the ATI or Geissman lamps. Other than that, the Current lamps work fine. But I think that just the exta output alone would be worth the little bit extra cost in lamps (40 - 50 bucks more to replace the lamps in the 8 lamp fixture with Geissman vs. Current every 18 months - 2 years isnt too bad at all really).