I use them in my tank. I don't use CO2 and only light dose so my growth is adequate, not super fast. They aren't as good as standard bulbs, but are cheap to work with for sure. A good reflector is a must as their shape throws light everywhere.
Those bulbs do work, but not nearly as well as their wattage would lead you to expect. I have 40 watts - 2 20 watt bulbs - over a ten gallon tank, with good reflectors, and it is far from high light intensity. In fact it is barely more than low light intensity. One thing this means is a lot of heat comes from the bulbs for a given amount of light.
I would rather use multiple T8 bulbs than use the screw-in CFL bulbs. The CFL is a cheaper and easier setup, but the long T8 tubes do a much better job lighting the tank, in my opinion. But, I really do like AH Supply light kits better than both of them. And, they do cost more too, but I found that I ended up spending as much for a multiple T8 bulb fixture as I did for an AH Supply kit - all of the detail pieces add up to a lot of money when you put together a multiple tube light.
I use CFL's in my signature tank below, Check out the thread for a photo of the hood and lights. They work well for me, I do end up running more total wattage and heat to get the same effect of a more expensive set up, but this works and I love projects so I try to DIY as often as possible, even if I don't really need to...