I've been (strongly) considering purchasing some Westcott Spiderlite TD5's to go inside soft boxes for fill and key lights. The fluorescent options look great, and with all the bulbs on, Westcott says the output will be comparable to more than 900 watts from my tungsten lights.

I've mostly been using a 1,000 watt tungsten lamp inside a medium Chimera soft box as a key, so the 900 watts (equivalent) should get close to the output.

The daylight color temperature and the cool environmental temperature are quite tempting.

Have you used these lights? If so, did you like them? Any downsides?

FYI -- I'd be using them mostly for talking head / interview style shots.

I called Westcott and spent some time with them on the phone getting some questions answered. Anyway, I ordered three of the Spiderlite TD5's. They should arrive Friday. Once I've put them to good use, I'll post my thoughts.

I'm expecting good things based on what I've heard and read...

Probably a bit late for this now....
We bought one some time ago to go inside a Poker Light (think that's what it's called). The unit is pretty heavy as it's cast metal so it is robust. Aside from that no real pros or cons to it. I'm not 100% convinced this is the most efficent way to get a lot of light into a softbox though.
The tornado style CFLs are not very long and end up very close together so I think a lot of the light coming out of them is just lighting up the nearby lamps rather than going into the softbox.